Ok, but first decide if you are saying “you” or “we”. For the answer, you can say: “Where are you going to spend the night?” Or “Where will you spend the night?” Both are correct.

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Good question! I am not quite clear whether this is two people discussing it themselves - where will we spend the night? - or a third person asking them - where will you spend the night? Assuming the first situation then both seem ok to me, using 'going to' or 'will'. However, the people are a bit shocked and surprised. This is similar to someone having their bag and money stolen, what they might say is 'What am I going to do now?' So 'Where are we going to spend the night?' seems more natural. (Actually 'What are we going to do?' is more likely because there is no obvious place to stay.) I can imagine someone asking themselves 'Where WILL we spend the night?' like they can't believe there is nowhere to stay. In the same way 'Where SHALL we spend the night?' would be possible. Another thing thing to consider is that in this situation the word f*** is likely to be used! Where the f*** are we going to spend the night?' seems more natural. Anyway, I don't think there is a clear answer even though some grammar books might say so.