Unfortunately, there are no "etiquette" related questions, at least, on the CA Boater Card nor on USCG courses for recreational boaters (that I can recall). I possess the CA Boater Card and USCG certifications.
I have been boating since 1980. It just dawned on me that I have split the last 44 years of boating between sailing vessels and power driven vessels almost in half. I sailed exclusively between 1980 and 2000. Then I moved inland (approx. 100 miles from coast) in 2000 and started power boating (local sailing in smallish lakes/reservoirs just wasn't the same as ocean sailing).
Since 1980, I took USCG classes and received certifications in Navigation and Sailing Skills and Seamanship.
In all of my courses (USCG and CA Boater Card) and other formal learning, I have never seen or have been asked questions, on any exam, about "etiquette."
KPH/MPH, oncoming vessels, right of way, and other safety precautions are abound in most formal boating and education courses. They are based on local, state, and fed laws/regulations.
I rented a boat once in AZ and was required by the local vendor to take a 45 min safety course before I could rent a boat, regardless of my USCG certifications I did not yet have my CA Boater Card). This course was not required in other rental facilities throughout AZ at that time, hence local requirements.
I agree that boat owners and rental boat vendors need to have some sort of safety (and etiquette) course requirement. As of 01-01-25, ALL CA boaters, regardless of age, will need to possess the CA Boater Card while operating a motor driven vessel. This requirement may be the first in the US.
Not sure how to tackle an "etiquette" requirement for boaters. Perhaps it is similar to driving. Some drivers are conscientious and courteous... and some will simply flip you off!