please enlighten me, who are the Goddesses,having skull-cup in one
Goddess Kali has numerous forms such as GuhyakAli, SmashAna KAli, Bhadra KAli, ShyAmA KAli, Dakshina KAli etc. The disciples who are initiated into the Bija mantra Krim, shall have to worship the Goddess with the following Dhyanam:
ShavArudhAm mahAbhimAm ghoradamshtrAm varapradAm |
trinetrAncha kapAl katrikA karAm ||
pivantim rudhiram muhuh |
Chatur vAhu samAyuktAm varAbhayakarAm
So, in this form the Goddess is holding a skull-cup in one of her hands.
KapAl katrikA karAm -- holding skull-cup and katrikA (a kind of bent sword like weapon)
Also, KapAla hastam is not the same as Vara abhaya karAm (even the DhyAnam I have given has this description). Vara Mudra etc are postures of hand where as Kapala Hastam signifies that she is holding a skull-cup in one of her hands.
Vara Mudra - Boon-granting hand postures; Abhaya Mudra - Mudras dispelling fear (of the devotess).
Source - Ahnika Krityam, Prathama BhAga - edited and commented upon by Sri Shyama Charan Kavi Ratna Varidhi.
I have checked her DhyAnam (Om kAli karAla vadanA .. etc - the one used during Sandhi Puja of Durga Puja ) and she is not depicted as holding a skull-cup in it.
She is the 2nd MahAvidyA and she is holding a skull-cup in one of her 4 hands.
Nila Tantram's 4th Patalah has the DhyAna Sloka from which we get:
Khadaga katri samayukta savyetaram bhujadvayAm |
samyukta savyetarabhujadvayam ||
Therefore, the 4 hands are holding a Khadga, a Katri, a lotus and a skull-cup.
For this form of the Goddess, there are many mantras and hence many DhyAnam. In some of those forms, she is having a Nara KapAla.
HAsyayuktAm trinetrAncha kapAlakatrikAkarAm || (TantrasArah;
So, one hand is holding the kapAla.
Katrincha kharparanchaiva kramAdvAmena vibhrati || (Viswa SAra
Kharpara is nothing but a half-skull.
She is another Goddess who's having the skull cup.
ArdgendumaulimarunAmamarAbhivandyAmambhojapAsha srini purnakapAla
Ucchista ChandAli MAtangi:
She is also holding it.
KapAlakatrikAhastAm param jyotiswarupinim || (TantrasArah)
She has four arms and she is holding it in one of her right hands.
Shulam kapAlam dakshe tu vAme tu pAshamankusham || (TantrasAra;
None of them have it like ChinnamastA, Bhairavi, BagalAmukhi etc.
Jaya DurgA, Sulini DurgA, Mahishi mardini, AnnapurnA, TriputA ---- None of these deities also hold a skull-cup (checked their DhyAnam).
Significance of holding a skull in the hand:
According to Srimat Swami Paramatmananda Natha Bhairava (Giri):
"The aspirant needs some amount of dispassion (Vairagya) in order to progress in the path of spirituality.
And, the end destination for a human being, who's having all sorts of desires etc, is in the cremation ground, and in the form of a Nara-kapAla (skull).
By holding the skull-cup, Goddess is helping to cultivate a sense of Vairagya in the aspirant's mind".