The title is a bit over dramatic but, per the title, if you could contribute with one piece of knowledge to a book that every single individual should learn from in order to kickstart a civilization, what would be yours?
My personal choice would be the process of soap making, from scratch.
I’m so far from an expert it’s not even funny but I’m a hobbyist for old valve (tube on the other side of the Atlantic) electronics. You need an industrial base to make semiconductors but if you can do flamework with glass and build a good enough pump that opens the door to amplifiers, radio, telecommunications, and even crude computers which in turn opens the door to a lot of creature comforts and social improvement that wouldn’t otherwise be possible.
Electronic valves are still a thing?
I had relatives that swore on radios based on that technology could endure the detonation of bomb and still work flawlessly.
And I had a colleague in school that saved up to be able to buy a valve based guitar amplifier.
Yeah the guitar amp and vintage HiFi markets keep a few types (mostly power triodes and pentodes but also preamp valves and even a couple of rectifiers) in production, largely in the former Eastern Bloc. There’s a few people on YouTube making their own too.