Ask HN: What to learn over the summer?

Continuing to look for ideas on what to advise my university-bound kid (going for CS) to focus on learning over the summer. The idea is to provide him with a way to have access to work above minimum wage by investing the summer coding.

In the context of a young person starting out, which of the various full stack technologies would provide the most opportunities and earning potential (part time/gig type work)?

I use Python/Django but not sure this would be the best given the stated goals. From a CS perspective it would probably be best for him to get really good at Python. Maybe that's reason enough to take that path?

Is there a nice (and reasonably lucrative) Wordpress-centric work ecosystem out there? Would that be a good thing to focus on rather than traditional full stack development? Or is WP development dominated by offshore programmers?