Why use "vos"? The straightforward translation of "Where are you"? Is "Ubi estis?".
It seems a little strange that every question we've seen up to this point has the question word placed first, Quot, Quo, Ubi, Quanti, Unde, etc. Then suddenly, boom subject before question word. Flagged it, but came here to provide explanation just in case justification is needed.
After briefly checking the DCC page, all examples listed had the question word first. So wanted to confirm that this may be an error. http://dcc.dickinson.edu/grammar/latin/questions