"Ever" means throughout the whole time period. In this case, it would be the whole life of the person you are asking. Therefore, you cannot use "ever" with other time words/expressions such as "latest", "in ten years" .. etc.
So you can say:
What is the funniest book you have ever read ?
What is the latest book you have read ?
What is the scariest book you have read in ten years ?
Student or Learner