Some of it is academic study (BS and MS at Georgia Tech) -- that helped with the theory and a bit of the breadth. That said, most of what I know of modern virtualization was more or less "on the job" from working on Google Compute Engine. Lots of practical experience understanding virtualization boundaries, and really really enormous access to historical domain experts in the space.

Depends on your country, but I suppose it has to do with theoretical computer science at the master level, you can see a lot of academic content around this (in Paris, France for example): https://wikimpri.dptinfo.ens-cachan.fr/doku.php (yes, HTTPS is broken…)