You are talking about what are known as rhetorical questions. The form is the same as any other question, including the question mark at the end. The idea is often to make the other person think about an issue e.g. What can we say about the issue of global warming? In my view, ... e.g. Do you always drive below the speed limit? I didn't think so You can use them for praise, especially for a young child or a pet e.g. [The dog catches a ball] Who's a clever dog now? e.g. [A baby smiles cutely] Aren't you the cutest child? Yes, you are.... You can use them for irony e.g. [Your team loses a match 7-0] Well, wasn't that a wonderful effort then? There are probably other uses too.

I wrote this answer before Michael Chambers posted his answer, so you can think of it as just an addition to and confirmation of what he has already written. In my opinion, writing “Aren't you the clever one." is incorrect, because it IS a question. You have to add a question mark. But a question can be rhetorical and thus be used as a statement. I would never personally say such a thing as ”Aren’t you the clever one?”, it could all too easily be interpreted as sarcasm or criticism. I don’t know if anyone actually says “Aren’t you the clever one?” in real life. It sounds like something a bully or a mean character would say in fiction/films/TV.

Chino Alpha. There is apparently some disagreement as to how a rhetorical question should be punctuated. It seems to me that both Michael Chambers and I agree that rhetorical questions should be punctuated with a question mark. This is what Wikipedia says: “Depending on the context, a rhetorical question may be punctuated by a question mark (?), full stop (.), or exclamation mark (!), but some sources argue that it is required to use a question mark for any question, rhetorical or not.” So you may see people writing rhetorical questions without question marks. "Won't I be glad to see the last of him". is a rhetorical question, but the writer of the sentence decided to use a period. I would have used a question mark.

Here's another example: 'Where did Alice put my phone?' 'How should I know?'