Look in the footer. It’s a Creative Commons Attribution license for all web.dev content and Apache 2 for all the code samples. I’m really not sure what else you would ask for here

My bad, the code is also on Github.

However it's far from a wiki and the process looks boring and cumbersome: https://web.dev/handbook/quick-start/

FWIW, here's a typical edit to an existing article: https://github.com/GoogleChrome/web.dev/pull/3678