I was watching NHRA drag racing and was wondering if most of the drivers knew how to diagnose issues or replace parts in the engine , or are they just top notch operators ? I realizes that they have pit crews and such but I saw one drive working on his car between rounds and didn't know if that was typical.
I don't know how typical it is in the pros, but yes, most can work on their cars.
Anyone who works their way up from small time racing to pro racing will know how to work on cars, because when you're first starting out, you don't have a team of pro mechanics.
If you've ever seen rally racing, there are typically 4-5 stages in between service stops. If something foes flat or worse yet breaks out on the course, the driver and co-driver not only have to be able to diagnose the problem, they have to then decide whether it can still be driven on to complete the given stage or can wait until between stages, and then they have to be able to work on it themselves.