Is "don`t you"possible?
I cannot think of a situation where it would. JSTE is strictly BÝT = to be in plural/formal 2nd person. Don't you? could work with any other verb with exceptions of TO BE and TO HAVE.
Wrote "Are you not?" and was marked incorrect.
Who knows, it is one of the accepted answers. Use "My answer should have been accepted" next time and we might be able to tell you more.
The narrator clearly say nejsou, but the correct answer is given as nejste.
I can only hear a clear "Nejste".
"Not you?" was marked incorrect.
You have no verb in the sentence.