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.
There is some evidence presented in David Graeber’s last book that Natives of Northeast America already knew all this wisdom after learning the hard way from the collapse of the earlier empires on the Mississippi hundreds of years before white people arrived. Then when we showed up, they went oh no, not this bullshit again.