The universal form of Krishna is an allegory to explain to mankind what enlightenment, self realization is all about.
When a soul atman, the spirit within reaches its cosmic end, 8.4 millionth manifestation it is free to travel to any part of cosmos at will. The whole cosmos is now at tips of an enlightened one.
When an enlightened one leaves mortal frame, it becomes free from all bondages including that of sun and finally reaches state of moksha salvation.
For an enlightened one visualizing entire cosmos was not difficult. One finally realizes what God Almighty; the entire cosmos was all about.
Allegorically Krishna depicts an enlightened soul, a liberated soul. Krishna is soul atman existing in all human beings. We can reach our Krishna within by becoming 100% truthful.
The real Krishna cannot be seen similar as we cannot see God. Krishna as a soul atman was part of God Almighty, Brahman. If an individual grain of sand is an independent soul atman, Krishna then the whole mound Brahman, God Almighty.
If an individual piece of puzzle is Krishna, an independent soul atman then the completed puzzle Brahman, God Almighty.
Anyone world over seriously desiring to see Krishna in reality must indulge in spirituality as detailed in Bhagavad Gita. Only then one could reach state of absolute purity as a soul atman.
Journey of spirituality demands demolishing of ego in totality. Furthermore to establish total control over five senses and mind we need practicing absolute celibacy for a minimum period of 12 years in continuation. This also results in full awakening of kundalini shakti, the coiled Serpentine energy lying dormant in base of spine.
Full awakening of kundalini announces one becoming an enlightened one, a bodhi, a Jina forever. To become a pure soul atman, a Krishna… full awakening of kundalini is an absolute must.