As a basic question, they mean the same thing. They both mean: Are you able to speak English?

Do you speak English = it means "Do you know how to speak English" Can you speak English = it means " Are you able to speak English" "CAN" is used to express the ability to do something.

In everyday English, they would mean the same. But getting a bit more technical, can means to "know or understand" while do means "to perform." So, one might "know" English, but not be able to "perform" it.

What's the difference between "Do you speak English" and "Can you speak English" ? 'Different' is an adjective while 'difference' is a noun. So, the correct form is 'What's the difference'.