You will hear it everyday in Brazil.
And for some reason, it's not presented in any of the Brazilian Portuguese grammar books or other learning materials! Probably because it's relatively recently become part of the common (conversational) vernacular. But it's omnipresent.In conversational Portuguese, Brazilians will use CADÊ in place of onde está or, aonde foi? extremely frequently. It's not slang -- it's become part of the language*
The pronunciation is like você in that the 'e' is pronounced 'AY': CA-DAY
Let's see it in action:
> Cadê você? Where are you?
> Cadê meu carro? Where’s my car?
> Cadê seu telefone? Where’s your telephone?
> Cadê a tua irmã? Where’s your sister?
It evolved from o que é de…? >> que é de? >> quedê? >> cadê?