Beyond the multitude of Universes and Celestial Realms is Goloka the supreme abode of Krishna. is it located before Nirguna Brahman or after Nirguna Brahman ?
A very good question. You want to know the relationship between Goloka and Nirguna Brahman. There is no relationship.
Goloka is the eternal loka or place for those who follow Bhakti Yoga and worship Brahman with form.
Brahma said, ‘…The two regions of felicity, viz, Goloka and Brahmaloka, became his upper and lower lips.’
Mahabharata Santi Parva Section CCCXLVIII
People who aim for Nirguna Brahman do not attain any loka. They just become Brahman.
There is no good explanation of the difference between the two either in scriptures or in the commentaries of ancient Acharyas. I am giving below the explanation that I find useful.
No one can say with finality that God is only 'this' and nothing else. He is formless and again He has forms. For the bhakta He assumes forms. But He is formless for the jnani, that is, for him who looks on the world as a mere dream. The bhakta feels that he is one entity and the world as another. Therefore God reveals Himself to him as a Person. But the jnani – the Vedantist, for instance - always reasons, applying the process of 'Not this, not this'. Through this discrimination he realizes, by his inner perception, that the ego and the universe are both illusory, like a dream. Then the jnani realizes Brahman in his own consciousness. He can not describe what Brahman is.
Do you know what I mean? Think of Brahman, Existence-Knowledge-Bliss Absolute, as a shoreless ocean. Through the cooling influence as it were, of the bhakta's love, the water has frozen at places into blocks of ice. In other words, God now and then assumes various forms for His lovers and reveals Himself to them as a Person. But with the rising of the sun of knowledge, the blocks of ice melt. Then one doesn't feel any more that God is a Person, nor does one see God's forms. What He is can not be described. Who will describe Him? He who would do so disappears. He cannot find his 'I' anymore.
The Gospel of Sri Ramakrishna, The Master with the Brahmo Devotees (I), October 28,1882
Goloka is in the region of the icebergs. Those who attain Nirguna Brahman stay in the open formless ocean.