Why can’t Sally and her friends drive? Correct

Why Sally and her friends can’t drive? Incorrect

Here are noun clauses used as an object. Notice that noun clauses do not invert the subject and the verb or auxiliary.

I don’t know why Sally and her friends can’t drive. Correct

I don’t know why can’t Sally and her friends drive. Incorrect

If you are asking a question you say Why can’t the person do …..etc. If it is a statement you would say The person can’t do ….etc. and you are not asking “why”.

Also can’t is a short version of cannot….means unable to do something…..other words like won’t, etc. have different meanings. Your verb usually follows the subject but not always. “can’t do, can do are part of your verb…but don’t have to be together in the sentence.

“Why Johnny Can’t Read” is the title of a book. “Why Can’t Johnny Read” wouldn’t have the same emphasis, I think.

I think you’d use “Why Johnny Can’t Read” if you were going to follow with the answer — for example if you’re writing a book, an article, or giving a speech. It would sort of define what your subject matter is going to be.

You’d use “Why can’t Johnny read?” if you’re actually asking the question of someone else, and would like to know what they think.