What are the positions in tech that will still be in hot demand in the next 20 years? How will it take one to acquire the skills, and where can one go to acquire those skills?

Those positions that require human thoughts and ingenuity to solve. Positions that require a high degree of mental agility combined with a passion for learning have proven to be quite resilient over the decades

Here's the problem. As you grow older most people learn at a slower pace or refuse to learn much at all. You have to literally discipline your brain to keep learning, even at a slower pace.

All this is far easier said than done. So don't think so much about positions as much as broad fields of study. Healthcare, Arts and technology all fit the bill when combined with both drive and passion for those fields but suck hard when you lack either.

Good luck with the career aspirations.