"On which balcony?"
Translation:Su quale balcone?
Because "sul" means "on the", and that's not what this phrase is saying.
Quale is the singular and quali the plural, gender invariant. Qual is the truncation of quale; in the past it was very used, while nowadays it's mostly idiomatic: I'd recommend using it before any word starting with "e", in most other instances the untruncated form works as well.
It's a phenomenon, also known as apocope, that causes parts of a word to "go missing" (http://en.wikipedia.org/wiki/Apocope); for instance "amore" can become "amor", "signore" becomes "signor", "uno" becomes "un", "quale" becomes "qual" and so on.
A similar, but fundamentally different phenomenon is elision (http://en.wikipedia.org/wiki/Elision); unfortunately when that happens in Italian it's also called apocope. Parts of the word still go missing, but the apocopic form and the following word are "joined" and become like a single word: this is signaled by separating them with an apostrophe instead of a space: l'albero (l' was lo), l'erba (l' was la), vent'anni (vent' was venti)...
To complicate things, the apostrophe is also used in the first case, when a whole syllable or more are truncated: poco becomes po', bene becomes be', and so on. In this case, though, there is no joining, so there might not even be a word after it, or if there is you need a space after the apostrophe to divide them.
An Italian article about it can be found at http://www.grammaticaitaliana.eu/elisione_troncamento.html
A neat list for all these forms is at http://en.wiktionary.org/wiki/Category:Italian_apocopic_forms
OMG, I need to say: "for instance "amore" can become "amor", "signore" becomes "signor", "uno" becomes "un", "quale" becomes "qual" and so on." OMG, so that's really where Portuguese came from, my dear God. We have the words Amor, Senhor, Um, Qual, all read just like those you quoted. I'm impressed. OMG, Italian <3