Asking if you are lacking of something

[Robmars]

Asking if you are lacking of something after you've shown your abilities to someone in purpose to give you a critique, how do you say it?

Where am I lacking?
what do I lack of
what am i lacking of?

[Beeesneees]

Where am I lacking? (in what area am I lacking?)
or
What am I lacking? (What aspects am I lacking?)
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Cheers m' dears!

[Robmars]

So both of these questions are grammatically correct? How about the question: What do I lack of? Is it grammatically correct?

Oh yeah to be more in detail, I should use "in what area am i lacking?" instead of just asking "where am I lacking? It is just like the person I'm asking to will probably ask more details, so he can answer specifically.