Hi @zeeltr1
Nice you are trying to go for the Adobe Experience Manager Sites Developer Professional Certificate.
Together with some other Developers, I created the questions for the renewal Professional Exam.
Following the training courses from Adobe is a very good start in my opinion, like that you get used to all the different functionalities and features that Adobe Experiece Manager Sites provides.
I see you are worried about your AEMaaCS knowledge, I wouldn't worry to much. If you look it from a developer point of view, creating a component for example is not different for AEM 6.5 then it is for AEMaaCS. So a lot of the things you already did during the Training Course will also be valid for AEMaaCS. The only thing I would recommend doing, is going through the guide to migrate from 6.5 to AEMaaCS.
The only additional tips I can give is keep practicing and preferabbly on a real project, there are always stuff you can't really learn from a training course.
If you don't have that possibility, try to come up with new components, recreate existing Core Components and see how Adobe did it (you can find the implementation of those here), implement things in different ways, etc...
Good luck with your exam!
Greetings
Rik