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 would write an overview of extended mind theory, an introduction to human cumulative culture, knowledge engineering and TRIZ.
The history of human civilization is riddled with challenging problems, solving which takes more than multiple human lifespans worth of effort. Having a good learning resource about the most advanced methods and tools for navigating these problems would be a huge help, I think.