Its quite confusing to me whether to use singular or plural verb in the above sentence. Will that be depending on the Subject "you" based on if it is singular or plural? Can anybody enlighten me?
It's always You are ..., You do ..., You have ... (as far as auxiliary verbs go).
So in your example, use When do you ...?
As Wikipedia says,
In standard English, you is both singular and plural; it always takes a verb form that originally marked the word as plural, (i.e. you are, in common with we are and they are).