Why not "Cum noi facem supă"?
"Noi facem supă." is an affirmative sentence.
"Cum facem noi supă?" is an interrogative form, with emphasis to "noi" that is ussually understood. Here the word "noi" has the role of emphasizing the local specifics.
I think that it is for emphasis; but I do not know why 'Cum noi facem supă' is not accepted'.
I understand that 'facem' presupposes 'noi' but it is surely not wrong to include it.
It is not the right order. The rule is: after all ”wh” English words you have a verb. If you want to exercise: https://quizlet.com/_7jxsvs?x=1qqt&i=2hwq4u