I have never heard of any debate moderators ever providing the candidates the questions prior to a debate. Doesn't matter if it's a presidential debate, Senatorial debate, Gubernatorial debate, Mayoral debate, High School class president debate, or any other type of debate. Candidates do not know what the questions are going to be. Some debates are specific topics. For example, there may be a debate that will only cover international topics. In that particular case the candidates might know in advance the topic, but not know the specific questions to that topic. When candidates are preparing for a debate, they will obviously try to predict and anticipate what the questions are going to be. If you are provided the questions in advance, that wouldn't really be a debate.
Debates are used to test your knowledge on various topics and issues. Debates are also used to test your ability to think on your feet. That's the reason debaters are not provided the questions in advance.