Swift and/or React Native. Mobile apps are good.
How to use some basic ML in practice. TensorFlow based NNs would be good.
How to use the ShopBot at my local hacker space. Also how to use the laser cutter to make cooler shit than I already do.
How to sew. I want to make some one-off items but really don't know much about sewing beyond the real basics.
How to use a bullwhip India Jones-style.
Surfing.
Bonus: welding, how to change brakes on a car, how to rebuild a carburetor, how to make kombucha, how to keep bees.