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.
Some of the inventions that historically took way longer than you’d expect: the shoe, the wheelbarrow, and the stirrup.
Also archival techniques so that history’s not as messy the next time around.