Question

what is the difference between. don't I speak English? and do I not speak English? ​

Answer 1

meaning is same....but structure of sentence is different

Answer 2

When you say "she doesn't speak English." You're saying she doesn't know English but she could learn it if she wanted to. When you say "she can't speak English." That means that she's either given up on English or there is something prohibiting her from speaking English.