Recently passed COSA with 95%. Sharing my study experience as there are few recent posts on here regarding COSA exam content.
I worked through Bob's CPL Air Law textbook which covers all of the information for COSA. As he suggests, don't just memorize the answers but refer to (and have an understanding of) the reg that each question is based on. Also read through the AIP to understand any regs in detail that the book summarizes. Knowing where to find certain information in the AIP is helpful when you are limited to 15 tags for the exam
I had read on another website that you need to study Met thoroughly to pass this exam. That isn't necessary in my opinion as the Operational Meteorology section in the Air Law textbook covers all the met q's I came across on the exam. AIP Gen 3.5 is also full of Met-Law type information.
After working through the textbook, I debated buying the additional online practice exams but decided against it. I'm sure they are helpful but if you are getting the textbook practice q's mostly right then I don't think it's a necessary expense.
Questions that I received on my exam were related to:
Separation minima for t/o and landing
VMC minima for different airspaces
CAO 48.1 - specific questions on appdx. 1,4,5 as I've seen Bob write on here *but* be familiar with definitions that apply to other appendices
Commercial ops (CAR 206)
Tracking tolerances (visual as well as when using radio nav aids)
Daily and Preflight (pre taxi vs pre takeoff) inspections
Thanks very much to Bob for a very useful textbook that covers the COSA exam content!