"From Middle English wherfor, wherfore, hwarfore, equivalent to where- (“=what”) + for. Compare Dutch waarvoor (“what for, wherefore”), German wofür (“for what, what for, why”), Danish and Norwegian hvorfor (“wherefore, why”), Swedish varför (“wherefore, why”)."
Juliet is not asking the moon where Romeo is - she's bemoaning the fact that he is a Montague and she is a Capulet: Why did you have to be a Montague?
It drives me crazy every time I hear a performance (typically high school or amateur productions) in which Juliet asks "wherefore ART thou Romeo?" instead of the proper "wherefore art thou ROMEO?"
*sigh* The tribulations of an old English major...
Reposted from 2020 to add this interesting bit from The Shakespeare Guide to Italy:
There is no "balcony" in Romeo and Juliet. None whatsoever. Not only is the word absent from the play, it isn't a word to be found in any other play, Italian or not, by the same playwright. For that matter, the word "balcony" is not found in any of the poetry ascribed to the playwright either.The playwright's descriptions in Romeo and Juliet are clear: Juliet appears in every case, by the author's own words, at her "window."
More about this took later.