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 think the instructions for how to make soap would be less important to a civilization than why to make soap. Germ theory and basic hygiene practices would save a lot of lives.
I feel like we’re still working on this lol. The amount of people who don’t properly wash their hands is really nasty.