Like with any (jamf) training, you will be thought the things you need to know to pass the exam, one of the most important things i tell people who attempt an jamf exam is: make notes and make sure those notes are easily accessible, as most likely you will need them again at some point. Best of luck!

The 300 test gets more into scripting, so if you're not familiar with scripting, I would brush up on that prior to taking the class/test. 

How long have you been using JAMF Pro?  I found that when I went for my first certification (back then it was called Certified Caster Admin) I was able to do really well because I use the system all the time.  Since then I've taken the 200 and 300, and will be taking the 400 this year.

I don't know how they run the class online these days since when I took the 200 and 300 they were in person.  But what I did was every night after the class I would review the material and try to test out what I learned on a JAMF pro beta instance (sign up for that if you haven't).  Helped quite a bit so I could know where everything was.  

Just to let you know, I still have my 200 and 300 books that they provided with me at work and I still occasionally refer to them.  So what you learn in class will help for a long time.

There is only 5-10 points that can be missed due to script knowledge in JAMF300 Exam -  if you are asking about that. 90% topics are related to the web UI. It was like it around 2 years ago

but there are some critical parts in JAMF300 Lessons. You are going to learn basic script level such as loop, if etc. and actually most important part is curl. Because with CURL commands, you will able learn and run XML and JSON APIs. If you are planing to get JAMF400, it's better to make some practise. Because you may have crazy requests from the management team and you'll unable to specify or create solution with standard Web UI. To create solution, you'll need scripting and API part.