I don't know what is what.
   →뭐가 뭔지 모르겠어요.
(뭐가 뭔지는 what is what또는 which is which)

※유사표현
I don't know what is going on.
뭐가 어떡게 돌아가는지 모르겠어요.

I'm totally in the dark.
오리무중이예요.

I'm totally confused here.
헷갈립니다.