what do you actually do on a jnco course?
There are a bunch of threads for this already, just have a search.
Alternatively, speak to your squadron staff as they should know, and it will vary depending on which Wing you are in.
Personally I did one recently in Surrey Wing. It was mainly lessons on leadership, conflict resolution, teaching lessons, and various other things you’d have to deal with as a Corporal, as well as a a section on calling/performing drill (which you’re assessed on) and 2 uniform inspections where they’re checking if you improve your uniform based on their advice. There’s also the well-known General Service Knowledge (GSK) test near the beginning. At the end of the weekend your mentor will review your performance over the course and a copy of the report will be sent to your OC who should discuss it with you as well. I can’t speak for other wings, but I’m sure they’re quite similar, feel free to ask if you have any specific questions.