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.
Since I mentioned it in a response to another poster:
I would include everything I know (or had access to for the sake of this scenario) about germ theory. Admittedly my own off-hand knowledge is not much, but basic hygiene and sanitation and how to avoid getting sick would save a lot of lives. What germs are, how vaccination works, etc.
This needs way more upvotes