Spoiler: it scores pretty low but supports JavaScript, which is surprising.
PS: You could have gotten this answered more quickly by Googling.
https://nagekar.com/2018/10/testing-websites-on-kindle-paper...
I'm not aware of any comprehensive documentation on this subject though. I'd say that if the site works on your 7th gen paperwhite it will probably work for the majority of users, although there are definitely a few old units still out there from the ~2011 heyday.