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 was going to add “and notion of basic hygiene” but refrained from it as it be breaking my own guideline.
Amendement: one thing, with the necessary context to make understable to role in the civilization