wiki-says:

so'ham is an emphatic form of aham, the first-person pronoun ("I")

                            aham = I                             asmi = am

                         AHAM ASMI                            I       AM

and: wikisays...

"Some say that when a child is born it cries Koham-Koham which means Who am I? That is when the universe replies So'ham."

see also So'ham