"Wherefore" does NOT mean "where" as stated in the two previous answers.
The correct quotation is "Wherefore art thou Romeo?", and means "Why are you Romeo?", in a speech in which Juliet is philosophizing about names ("deny thy father and refuse thy name, O!, what's in a name?") and their meaning and significance ("that which we call a rose, by any other name would smell as sweet"). The underlying question is why their love should be forbidden just because they happen to belong to rival families in an old feud.
