Ask

Starting fire with just a couple sticks.

I guess basic home renovation suff. I literally do these kinds of things for a living. In my experience, it’s not so much that people don’t know how to do this stuff - it’s more that they lack the tools, the time, or they’d just rather pay someone to do it properly. I’ve had jobs where it took me only a minute to fix something they could’ve easily done themselves, but honestly, I can’t blame people for not wanting to mess with something they’re unfamiliar with. Most of the time, I’m not any wiser than they are at the start either - but I guess I just have the ability to figure things out on the fly.

Mental arithmetic

Chicken doesn't need to be covered in vegetable oil to be cooked.

Same as most kids don't know. there are a number of things. Money, listening, how/who to gather information from. I'm missing your point when you put adults in your question.

How to get to the bottom of a conflict without settling on popular opinion.

How to build a house.

90% of the work of building a house can be done by a semi-competent DIY'er. Learning the basics of framing, roofing, plumbing, electrical, drywall, etc, is not that hard.