The most famous line from William Shakespeare's Romeo and Juliet, is quite often misinterpreted. This is due to the differences between the Early Modern English of Shakespeare's time and its next evolution, our Modern English.
In this balcony scene, Juliet is not asking where Romeo is! She instead wants to know why Romeo is a Montague and she a Capulet (their families historically despise each other).
In this sense "wherefore?" is more accurately defined as meaning "for what purpose?"
Click here for a full breakdown of the famous balcony scene. Just in case you were confused by what "a rose by any other name would smell as sweet" means.