Could you be a little more specific? "Who is X" can be answered very simply with a name. More elaborately, with a list of common attributes (gender, age, height, job etc). But, more fundamentally, it can take a lifetime of introspection to try to comprehend the answer. Ultimately, one finally realizes that one has no idea "who" one really is! And, finally, that it doesn't matter. One should have simply lived - carpe diem -, instead of wasting one's precious time on fruitless metaphysical inquiry. But now it's too late. No time left for living, only dying.
So I'm afraid the question is too broad, as it stands, to address.
