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.
Good luck on that. For what we can tell, it is a part of our makeup. But we could aspire to less asinine systems of belief.
“Spirituality is not religion. Religion divides people; belief in something unites.”