If I am not wrong you are asking 2 questions here... 1st one being who is the twice born Purusha and the 2nd one is who is the living one comparable to this Purusha.
Ok As for Who is the Twice born Purusha it's Lord Shiva.
According to Ishwara Gita chapter 7.:
सावित्री सर्वजप्यानां गुह्यानां प्रणवोऽस्म्यहम् । सूक्तानां पौरुषं सूक्तं ज्येष्ठसाम च सामसु ॥ ७.१३॥ Meaning: - Among all the Japa (chantings) know me to be Savitri Mantra, among the confidential (elements) know me to be Pranava (Omkara). Among suktas (of Veda) know me to be Purush Sukta, among Sama (Veda) know me to ne Jyesth sAman.
The Taittirya Aranyaka(10:24:1) of Yajur Veda clearly says .:
Lord Rudra is 'Veda Purusha' (purusho vai rudrah).
Now how he is born twice.?
Hymn of the Supreme Being
~Holy Rigveda Samhita X:90:1-18
tasmād virāḷ ajāyata virājo adhi pūruṣaḥ |
sa jātoatyaricyata paścād bhūmimatho puraḥ || 5 ||
From Him Viraja was born; again Purusha from Viraja was born, as soon as He was born He spread eastward and westward o'er the Earth. 
This verse says that viraj was born from Purusha. Viraj is the Shining world. It is also called Hiranyagarbha by the Upanishads. The vedas call it by name Prajapati.. This Prajapati is responsible for creation. He is the first being to be born. From Prajapati, the Purusha himself took his birth. As soon as he was born he spread out over the earth in all the directions. ie., he multiplied and new species evolved.
Purusha ---------> Hiranyagarbha --------> purusha.
(Unmanifest) ( Visible universe) ( all living beings)
That's how the Purusha took birth twice. 1st he was self born from Nirguna to Saguna than again he was born from Viraja (Hiranyagarbha).
The same thing is mentioned in Atharva Veda while describing about ascetic form of Lord Shiva (Vratya):
vrā́tya āsīd ī́yamāna evá sá prajā́patiṃ sám airayat || sá prajā́patiḥ suvárṇam ātmánn apaśyat tát prā́janayat || tád ékam abhavat tál lalā́mam abhavat tán mahád abhavat táj jyeṣṭhám abhavat tád bráhmābhavat tát tápo 'bhavat tát satyám abhavat téna prā́jāyata || ( Atharva Veda 15:1:1-3)
"There was Vratya( Ascetic form of Lord shiva) . He roused Prajapati to action. Prajapati beheld gold in himself and engendered it. That became unique, that became distinguished, that became great, that became excellent, that became Brahman, that became Tapas, that became Truth: through that he was born."
sò 'vardhata sá mahā́n abhavat sá mahādevò 'bhavat || sá devā́nām īśā́ṃ páry ait sá ī́śāno 'bhavat || sá ekavrātyò 'bhavat sá dhánur ā́datta tád evéndradhanúḥ || nī́lam asyodáraṃ lóhitaṃ pr̥ṣṭhám || nī́lenaivā́priyaṃ bhrā́tr̥vyaṃ prórṇoti lóhitena dviṣántaṃ vidhyatī́ti brahmavādíno vadanti || (Atharva Veda 15:1:4-8)
"He grew, he became great, he became Mahadeva.He gained the lordship of the Gods. He became Ishana. He became Eka Vratya. He held a bow, even that Bow of Indra. His belly is dark-blue, his back is red( Nila Lohitam) . With dark-blue he envelops a detested rival, with red he pierces the man who hates him: so the theologians say."
So Atharvana Veda makes it clear that Rudra was there even before Prajapati and It was Rudra who created Prajapati and roused him into action. Later, He himself manifested through Prajapati and spread in all directions in form of in-dweller living beings and gods.
After creating the Universe (Hiranyagarbha) Shiva projects all the gods and creatures in various directions inside the universe. That is to say that he manifests into various forms of gods and creatures projecting them in all the directions.
The hymn on Vratya (Ascetic Shiva) in Atharva Veda which details out how Vratya (Shiva) transformed himselfinto various gods and manifested them from his form. Let’s see the verses now.
Shiva became the Marut host:
“sá yát prā́cīṃ díśam ánu vyácalan mā́rutaṃ śárdho bhūtvā́nuvyàcalan máno ‘nnādáṃ kr̥tvā́ |” (Atharva Veda XV:14:1)
“He when he went away to the eastern region, went away having become the Marut host, and having made Mind an eater of food”.
Shiva became Indra:
“sá yád dákṣiṇāṃ díśam ánu vyácalad índro bhūtvā́nuvyàcalad bálam annādáṃ kr̥tvā́ |” (Atharva Veda XV:14:2)
“He, when he went away to the southern region, went away having become Indra, and having made Strength an eater of food”.
Shiva became Varuna:
“sá yát pratī́cīṃ díśam ánu vyácalad váruṇo rā́jā bhūtvā́nuvyàcalad apò ‘nnādī́ḥ kr̥tvā́ |” (Atharva Veda XV:14:3)
“He, when he went away to the western region, went away having become King Varuna, and having made the Waters eaters of food”.
Shiva became King Soma:
“sá yád údīcīṃ díśam ánu vyácalat sómo rā́jā bhūtvā́nuvyàcalat saptarṣíbhir hutá ā́hutim annādī́ṃ kr̥tvā́ |” (Atharva Veda XV:14:4)
“He, when he went away to the northern region, went away having become King Soma (Moon) and having made the Seven Rishis’ oblation an eater of food”.
Shiva became VISHNU:
“sá yád dhruvā́ṃ díśam ánu vyácalad víṣṇur bhūtvā́nuvyàcalad virā́jam annādī́ṃ kr̥tvā́ |” (Atharva Veda XV:14:5)
“He, when he went away to the stedfast region, went away having become Vishnu and having made Virāj an eater of food”.
Shiva became Rudra (the deity responsible for destruction – kAlAgni rudrA):
“sá yát paśū́n ánu vyácalad rudró bhūtvā́nuvyàcalad óṣadhīr annādī́ḥ kr̥tvā́ |” (Atharva Veda XV:14:6)
“He, when he went away to animals, went away having become Rudra and having made herbs eaters of food”.
Shiva became Yama:
“sá yát pitr̥̄́n ánu vyácalad yamó rā́jā bhūtvā́nuvyàcalat svadhākārám annādáṃ kr̥tvā́ |” (Atharva Veda XV:14:7)
“He, when he went away to the Fathers, went away having become King Yama and having made the exclamation Svadhā an eater of food”.
Shiva became Agni:
“sá yán manuṣyā̀n ánu vyácalad agnír bhūtvā́nuvyàcalat svāhākārám annādáṃ kr̥tvā́ |” (Atharva Veda XV:14:8)
“He, when he went away to men, went away having become Agni and having made the exclamation Svāhā an eater of food”.
Shiva became Brihaspati:
“sá yád ūrdhvā́ṃ díśam ánu vyácalad bŕ̥haspátir bhūtvā́nuvyàcalad vaṣaṭkārám annādáṃ kr̥tvā́ |” (Atharva Veda XV:14:9)
“He, when he went away to the upper region, went away having become Brihaspati and having made the exclamation Vashat an eater of food”.
Shiva became Sun god (Aditya) [From the name Isana shiva manifested himself as Sun as per Shatapatah Brahmana 6:1:3:17, so although Ishana is Shiva’s name, the below verse means Sun]:
“sá yád devā́n ánu vyácalad ī́śāno bhūtvā́nuvyàcalan manyúm annādáṃ kr̥tvā́ |” (Atharva Veda XV:14:10)
“He, when he went away to the Gods, went away having become Isana (Sun) and having made Passion an eater of food”.
Shiva became Prajapati (Note that in vedas Prajapati means Viswakarma not Brahma as he is the architect of the universe so also called as Prajapati):
“sá yát prajā́ ánu vyácalat prajā́patir bhūtvā́nuvyàcalat prāṇám annādáṃ kr̥tvā́ |” (Atharva Veda XV:14:11)
“He, when he went away to creatures, went away having become Prajāpati and having made vital breath an eater of food”.
(In vedas, Brahma is called as hiranyagarbha (golden universe) and viswakarma as prajapati. Though Brahma is also called as Prajapati but here Prajapati refers to Vishwakarma only.)
Shiva became Parameshthin:
“sá yát sárvān antardeśā́n ánu vyácalat parameṣṭhī́ bhūtvā́nuvyàcalad bráhmānnādáṃ kr̥tvā́ |” (Atharva Veda XV:14:12)
“He, when he went away to all the intermediate spaces, went away having become Parameshthin and having made Devotion an eater of food”.
Likewise Shiva created Earth, firmament (Sky), heaven, cosntellations, seasons, season-groups, year, etc.
So Lord Shiva at first created hiranyagarbha and and then after entering this hiranyagarbha he took the form of all the gods as non dual Advaita.
For more info on Purusha Shuktam see this answer of mine.
Now from above it's crystal clear that the twice born Purusha is none other than Lord Shiva. So now let's see who is that living one who is comparable to the twice born Purusha...It's Náráyána Rishi.
Narayana Maharshi was the 'Mantra Drashta'(seer) of the hymn. This Narayana Maharshi was later incarnated as Devaki putra Sri Krishna during Dwaparayuga. His counterpart Nara Maharshi was born as 'Arjuna'. By the grace of Lord Shiva, Narayana Mahrshi got the divine vision of Purusha. He was the first Human Rishi to realise the universal oneness and oneness of Atman in all beings. This non-dual knowledge made Narayana Rishi merge with Lord Shiva. Those who know Purusha will become, verily, like Purusha, the self of all beings.
Sathapatha Brahmana of Shukla yajurveda describes how Narayana Rishi became one with Purusha.
"puruṣo ha nārāyaṇo'kāmayata atitiṣṭheyaṃ sarvāṇi bhūtānyahamevedaṃ sarvaṃ syāmiti sa etam puruṣamedham pañcarātram yajñakratumapaśyattamāharattenāyajata teneṣṭvātyatiṣṭhatsarvāṇi bhūtānīdaṃ sarvamabhavadatitiṣṭhati sarvāṇi bhūtānīdaṃ sarvam bhavati ya evam vidvānpuruṣamedhena yajate yo vaitadevam veda" ( Sathapatha Brahmana 13:6:1:1)
"Purusha Narayana desired, 'Would that I overpassed all beings ! would that I alone were everything- here (this universe) !' He beheld this 'five days' sacrificial performance, the Purushamedha and took it and performed offering therewith ; and having performed offering therewith, he overpassed all beings, and became everything here. And, verily, he who, knowing this, performs the Purushamedha, or who even knows this, overpasses all beings, and becomes everything here."
In Mahabharata, Anushasana parva Bishma pitamaha says to Yudhistira:
Rudra bhakthya thu krishnena jagat vyaptham mahathmana,
Tham prasadhya thadha devam bhadaryam kila bharatha.
Arthath priya harathwam cha sarva lokeshu vai yadhaa,
Prapthavaaneva rajendra suvarnaakshan maheswaraath.
"The Krishna, due to his devotion to Supreme Lord Rudra, Has spread all over the universe, Oh Bharatha, Oh king of kings, After making Lord Shiva pleased by his penance in Bhadrinath, He has attained the state of being more dear, Than all the worlds and all aspects of knowledge."
“yuge yuge tu kṛṣṇena toṣito vai maheśvaraḥ।bhaktyā paramayā caiva prītaścaiva mahātmanaḥ॥” (MBH 13:14:13)
“In every new Yuga has Krishna (by such penances) gratified Mahadeva. In every Yuga has Mahadeva been gratified with the great devotion of the high-souled Krishna“.
In Mahabaratha, Lord Shiva says :
satyaśaucārjava tyāgais tapasā niyamena ca
kṣāntyā bhaktyā ca dhṛtyā ca buddhyā ca vacasā tathā ( Mh Bhar 10.7.60)
yathāvad aham ārāddhaḥ kṛṣṇenākliṣṭakarmaṇā
tasmād iṣṭatamaḥ kṛṣṇād anyo mama na vidyate ( Mh Bhar 10.07.61)
The below verse has been spoken by Veda-Vyasa in Mahabharata.:
“sa eṣa rudra bhaktaś ca keśavo rudra saṃbhavaḥ | sarvabhūtabhavaṃ jñātvā liṅge ‘rcayati yaḥ prabhum | tasminn abhyadhikāṃ prītiṃ karoti vṛṣabhadhvajaḥ |” (MBH 7:172:89-90)
“Kesava is that devoted worshipper of Rudra who has sprung from Rudra himself. Kesava always worships the Lord Siva, regarding his Linga emblem to be the origin of the universe. The God having the bull for his mark cherisheth greater regard for Kesava”.
"With truth, purity, sincerity, resignation, ascetic austerities, vows, forgiveness, devotion, patience, thought, and word, I have been duly adored by Krishna of pure deeds. For this there is none dearer to me than Krishna".
So by doing Purushameda yagna Náráyána Rishi became one with Supreme Purusha Shiva and became one with him. Because those who knows the ParamaBrahmana becomes Brahman themselves.
एकं सद विप्रा बहुधा वदन्त्यग्निं यमं मातरिश्वानमाहुः || (Rig-Veda 1:164:46)
ekaṃ sad viprā bahudhā vadantyaghniṃ yamaṃ mātariśvānamāhuḥ ||
God is One, wise call him by many names.
So, it is crystal clear that there is Only One Divinity (ॐ) which is denoted and praised by many names in Veda. Therefore, that Ultimate reality is One and Only One, which Veda praises under different names.
I hope it clear your doubts here.