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.
Professional scientist here. I would take a table of logarithms. In a world without computers, the logarithm table and slide rule are the essential tools of how things got built. We built the Golden Gate Bridge and put a man on the moon using nothing more than log tables.
Any one person can remember the gist of the scientific method and write it down on a page. To write down a quality logarithm table you would need 500 pages.