Heya! Sorry for the late reply, but hopefully this helps other folks with a similar question!
Whilst there is no simulator, you can find the F5 NGINX Certification FAQ here. It has a lot of valuable information to help you register for the F5 Certification program and to access NGINX Certification resources.
You can also find an example of a question below:
Note that this question was rejected and will not appear on any exam, but the question is similar in format to what you might expect to see when you take the exam. As of this point in time, all of the questions multiple choice questions. Sometimes there will only be one right answer, sometimes there might be multiple right answers. This is indicated in the question itself. There are no fill in the blank questions.