Aren't you don't teach me?" is incorrect. Here you want to use the present continuous tense, so you need the verb "to be". Aren't you going to teach me? You could also use "to do" and the present tense, but the sentence in this case wouldn't really make sense: don't you teach me? This sounds like you're asking if I teach you regularly. So the correct sentence is the first one (aren't you going to teach me?). Remember that are and do will never be found together :)