It's أنا أفهمك (standard Arabic) أفهم عليك is a dialect, I think.

if you mean that expression we say that is equivalent to "gotcha" or "I see" "I got it" "I understand" then I recommend saying فهمت عليك فاهم عليك عرفت وضحت لي

I understand you. أنا أفهمك ana afhamok.

i get it i see

انا افهمك او استطيع ان افهمك