"What do you understand?"
Translation:Vous comprenez quoi ?
Because que becomes quoi when it comes after a preposition, as we saw in the previous exercise:
Avec quoi mangeons-nous cette viande?
or when it comes at the end of a sentence, as this one:
Vous comprenez quoi?
"Qu'est-ce que comprends tu ?" is wrong. It can be "Que comprends-tu ?" or "Qu'est-ce que tu comprends ?"
You can't combine est-ce que with subject-verb inversion. It's one or the other, but not both at the same time.
this was answered above by MaPfe - "que" becomes "quoi" when it comes after a preposition or when it is at the end of a sentence, see her examples above. So you can either say "Que comprenez-vous ?" or "Comprenez-vous quoi ?"
Tt can be either, so if you got it wrong there may have been another mistake in your sentence. See answers above for some examples of correct answers.
This was answered above by relox84 - It can be "Que comprends-tu ?" or "Qu'est-ce que tu comprends ?", the first one forms the question using the inversion "comprends-tu", and the second one forms the question by adding "est-ce que". See the Tips and Notes for Questions for all the different ways that you can form a question in French: https://www.duolingo.com/skill/fr/Questions/tips-and-notes
It accepted "Que comprends tu ?" and said that "Vous comprenez quoi ?" was an alternate translation. Does changing the order of the words make one sound more formal than the other, or is there no real difference?
The system should also accept: "Qu'est-ce que c'est que tu comprends?" I reported it and would appreciate it if someone could explain to me why that response is not also correct.