There are two courses that are ArubaOS 8 related.
IAW - Implementing Aruba WLAN (3 day course)
SWDI - Scalable WLAN Design & Implementation (5 day course)
You should take IAW before taking SWDI.
I always recommend an in person class. You are less distracted and you will learn from the other students too. These courses are also offered in a virtual format. Instructor is live and you see their slides/screen and listen to them and can ask question.
CWNA is also an excellent source of knowledge. You can attend a course, or purchase one of the two study guides; one by Sybex and the other by CertiTrek (you can find them on Amazon; compare for yourself; my recommendation would be biased).
I hope this helps,