Hi Meghan, we sometimes use the present tense to express "future" like in this case, especially with "querer+infinitive". This lesson is about using either the subjunctive or the indicative after "cuando", that's why it needs the subjunctive. You could easily say this as well without changing the meaning: "¿Dónde querrás comer cuando salgamos esta noche?" but both options are expressing a future idea in the first part of the sentence. It sounds more natural to say in Spanish "¿Dónde quieres comer...?, that's why we chose that one.

I hope it helped.

Inma