I think if "What's on and Where" is used as a title to an article then the question mark seems appropriate. But if it's used as the header for a list then it doesn't need it.

I know the question mark is the most grammatically proper way to punctuate the phrase "Who knows?" but I feel the exclamation mark is the most logical punctuation. You are not really asking a question, rather answering your own: Do you need a question mark? Who knows! You are really declaring something. It's not even a rhetorical question. It's a claim. You are saying nobody knows. Maybe it should depend on where you use it. For example, it "feels" more proper to use a question mark if you follow it with an answer: Who knows? I don't!