"Di mana alamat mereka?"

Translation: What is their address?

[mosesoktavianus]

Is that wrong? What : apa, and Where: Di mana?

[TCdot]

I think "di mana" is for places like "berapa" for numbers.
i.e. "Jam berapa?" is translated into English as: "What time is it?"

[Pak_John]

Yes similar idea like "siapa nama kamu = what is your name" (Literally who is your name)