Can I use a question as a title for a persuasive essay? Ex: Is The American Dream Really Dead?

The hard and fast rule is that your thesis statement cannot be a question. You can say “The American Dream is dead” or “The American Dream is still alive” as a thesis statement. But for the title of your essay, a more appropriate choice might be “Investigating the American Dream” or “The American Dream: A Health Report.” Any essay assumes there will be some controversy surrounding the subject, with at least two sides available for argument, so the most sophisticated way to title your essay is to imply that, while you will be arguing one side in essay form, you acknowledge at the same time that there exists an opposing view.  While there is built-in rhetorical value in a question, and while a question is a provocative opening, the aim of a persuasive essay is to convince the reader that your point of view is logical (and irrefutable).