As far as Jeopardy goes, (this was in the pre-Covid days), they have regional tryouts. You and maybe a thousand other people play a few rounds, seeing how fast you can buzz in. If you do well, you get put on a waiting list (my wife made it on. It was at least a year) then you might get called. They’ll pay your air fare, but booking a hotel is up to you.
I haven’t watched Jeopardy in a while, but last time I checked Alex Trebek was going to step down, due to his health and his age.