Which video you are talking about
or
what video you are talking about 
or
which video you are mentioning

Ask anything if you need! 

which video are you talking about?

About which video are you talking?

Which video are you talking about?

which vedio are you talking about?

Which video is he talking about?

What video are you talking about man?
or
What video is he talking about?

you are talking about which video?