You have to phrase it as a question to get the money. When you buzz in you get something odd like 7 seconds to answer the question. If you just say “Eiffel Tower” then Ken Jennings will now probably just stare at you expectingly to rephrase your reply in that time. I think in the past Alex Trebek may have prompted candidates to rephrase their non-question answers but I haven’t seen that happening in a while (but I don’t watch it that regularly either so 🧂).

The whole point of the show is that the standard quiz show mechanic question->answer gets put on its head. The clue on the wall is the answer and the candidates have to provide a question it answers.