Gotcha is slang for "(I/he/she/they/we) got you", which means of course "(I/he/she/they/we) understood you".
I understood you = I got you = gotcha Right?
If I wanna ask a question. Did you understand me? = ....got or get.( you got it?) ...? = ....gotcha...? I mean how to use get and gotcha in question. How Is it possible?