The documentation is at https://developer.ww.wp.xz.cn/rest-api/ currently.
There’s no downloadable form, but it’s not too much to scrape or copy or print. 🙂
Out of curiosity, why doesn’t Automattic make any attempt to provide downloadable docs? There are billions of people around the world without internet, and millions in the United States that have to drive an hour to a rural library to get internet.
Automattic does not control WordPress: https://codex.ww.wp.xz.cn/WordPress_vs_WordPress.com
WordPress is free open source software, built and supported entirely by volunteers, and backed by the non-profit WordPress Foundation: http://wordpressfoundation.org/
I imagine that we don’t have downloadable documentation due lack of volunteers offering to do it.
If you’re interested in helping out with that, I recommend joining up with the Documentation Team: https://make.ww.wp.xz.cn/docs/
