This question is an exact duplicate of:
Currently, hovering the mouse over a Hot Network Question title does nothing (but show the URL in the bottom of the browser, if supported). Sometimes the title of the question alone doesn't make it clear what the question is about, like what programming language, or what fictional universe/work it regards. Clicking is the only way to know for sure.
Can hovering on the title of a question show the current tags of the question?