"What is your name?"
Translation:ʻO wai kou inoa?
If it's the beginning of an equational sentence, then the 'O goes at the beginning even if there is a ko'u, but as I understand it, anywhere else in the sentence you wouldn't use 'o before ko'u. Perhaps if you see a sentence with 'o before ko'u again, ask why in that sentence discussion because that seems, to me, to be the one not matching the patterns taught.
Traditionally it was pronounced with the lips tight so that they buzzed like a v, but without touching the lips to the teeth. I think these days you may find a variety that includes an English style w and an English style v. I think the tight lip buzz is probably still considered the most correct, but I'm just a student, too, so I'm not sure.