when I prepared for it some years ago, I mainly focused on the GMAT, paying a lot of attention to the time constraint.
Topics of the test include:
The questions are not super hard once you have understood the general logic. The most difficult thing – where many people fail – is the time management. You can find some sample questions at the link below:
As you pointed out, the test is 30 questions in 20 minutes, which means that you have less than one minute per question. Together with the fact that you get penalized for wrong answers, this implies that you should leave blank some questions initially. If you don’t do this you won’t manage to obtain a good performance.
When I did mine, I covered 23-24 questions, skipping 6-7. As I finished with a couple of minutes left, I went back to the previous questions, managing to complete 2-3 additional ones.
Hope this helps,