I am not sure if you are talking about the certification or Denodo training. If talking about trainig, from my point of view, the courses and exams that you will find in the "On-demand" training have a good level of complexity, as some questions are very easy and there are others that you would need to think and use official documentation to find the answer.
In my case I prefer not to have trivial courses/exams as I feel bored with them. I prefer a challenge as that makes things more interesting.
Anyway I would recommend you to get used to the official documentation, as all the information about Denodo Platform is there. You can use the "Search" button that is in the right-top corner of this screen for finding information in different documents about your specific topic. I use a lot this option as it help me a lot to find information that I need about Denodo.
Hope this helps!