I've been absorbing Japanese through osmosis for years, but I just started learning it formally. The app I'm using presented these two sentences with the same translation, I think just to show that the interrogatives like どこ can't take は as their particle:
病院はどこですか Where is the hospital?
どこが病院ですか Where is the hospital?
My question is, when would you use the latter? (My understanding is that the first is more normal.) What's the difference in emphasis?
I think I get the difference for a different interrogator. If I understand correctly, 先生はだれですか is neutral/putting emphasis on teacher, so it could mean "Who (among us) is a teacher?" Whereas だれが先生ですか puts emphasis on "who," as in "Just who is that teacher." (I'm overemphasizing the distinction.) But I don't see how that applies to どこ.