"Which is which" is correct.
A: On the plate in front of you are cheddar cheese and Gouda cheese.
B: I don't know which is which.
Student or Learner
Is it right to say "I don't understand, which is which or which is which's(in any context, actially I didn't come up with any sentence or scenerio for this formation, sorry)".Please help.
In any case can we also use "Which is which's"?