To me, it boils down to 2 things. One is fairly decent mechanical knowledge. The advisor does not have to be a top pro technician or anything like that but should have a very good understanding of what makes mechanical things tick. They should be able to talk with a customer, test drive the car, etc. and be able to at least make an educated guess at the problem.
The other thing is integrity. It’s one thing if an advisor cannot explain a problem technically but some of that Star Trek BS should never be used. If the advisor cannot explain something then have the tech put it into a few basic sentences noted on the back of the repair order.
The former could be very well illustrated by our local GMC/Jeep dealer. Their service manager (recently retired) would run ads in the paper to hire service advisors and a warranty clerk. The ads would always state “2 years of college required, computer proficient, and no mechanical knowledge or aptitude needed”. This is exactly what they would hire too.
JMHO, but this is NOT the type of person one wants in a position of trying to explain a car problem to the car’s owner.
I often mention a disconnect between the tech and the car owner; this is a classic example of it.