Things like this helps you learn because it teaches you to understand the sentence not just guessing what it is from the meaning.
Can I say "Sen kedim misin?" ?
Yes, I think so. You can even say ‘Kedim misin?’ since benim is should though the -(m)I ending attached to kedi (thus kedim - my cat) and _sen is shown to -sIn ending attached to mI (thus Sen benim kedim misin? = Kedim misin?).
Yes, you can say.
can i just say "kedim misin ?"
Love the questions in this lesson. "Are you my cat? Am I big?" No, but you might be high...
so when do i use misin and when musun??
It depends on the last vowel before misin/musun. Read about vowel harmony in Turkish.
Hayır, senin kedin değilim.