The only hard rule is that it be phrased as a question, which implies the rest of the phrasing is irrelevant as long as the answer is in the question. In your example, “Who is the Eiffel Tower?”describes it incorrectly but correctly names the tower and should be accepted, but “What is that famous tower in Paris, France?” describes the correct answer but is missing the critical answer and should not be accepted. Also, who/what/etc. is not required to be part of the question.

What’s … in a question? The rules state, “…all contestant responses to an answer must be phrased in the form of a question.” It’s that simple. Jeopardy! doesn’t require that the response is grammatically correct. Further, the three-letter name of a British Invasion rock band can be a correct response all by itself (“The Who?”), and even “Is it…?” has been accepted. So, Matt Amodio’s no-frills approach is unique but well with guidelines. jeopardy.com/…/what-are-some-questions-about-jeop…