I think I heard a few times people saying: Where do we go now? instead of "Where are we going now?" OR What do we do now? instead of What are we going to do now?

Why do they use the present simple instead of the present continuous?

going implies a plan. The point is that there is no plan. We are completely clueless about what comes next.
What are we going to do now? for example, implies that the person being questioned has a plan which he will reveal in his answer.

What do we do now? in contrast, implies that none of us has any idea how to proceed. An equivalent expression is Now what?
A father and his son are putting a bicycle together, following a set of instructions provided with the new bike. They are almost finished when the son notices that a crucial part is missing. He asks, "What do we do now?" or "Now what?"
These expressions almost always occur in situations of impasse.
That said, and just to make things more confusing, the son couldhave said "What are we going to do now?" Emotion: smile To my ear, this sounds more as if he thinks his dad will have a workable plan. But my ear isn't infallible, so wait and see if others have other opinions.

Hi. I guess it's more formal to say that way. Really you can use Present Simple (rather in formal way) in questions which imply instructions or guidelines to be given.
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 CalifJim's reply was promoted to an answer.
Your explanations make sense Calif Emotion: wink
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