It can be correct using either "which" (= which floor out of all the floors in the building) or "what" (=not really thinking about the other floors in the building. Over the phone, I'd usually say, "which / what floor are you on?" On the elevator, perhaps the sentence fragment, "which floor?"

Yeah, if you refer to where someone lives: On which floor do you live? Which floor are you on?

Hello Dayanne, How Ate you? I tried to send you a private message but this option is not available in your profile. Please, send me a private message to continue? I´m from São Paulo!! Do you live in Washington? How is your experience? Regards, Guilherme