there are at least three reasonably comprehensive open-source k implementations:

https://github.com/kevinlawler/kona (k3)

https://github.com/JohnEarnest/ok (k6, js-based)

https://codeberg.org/ngn/k (k6, c-based)

even today, many k programmers learn from the k2 reference manual. k2/k3 are extremely similar:

http://web.archive.org/web/20050504070651/http://www.kx.com/...

oK has a briefer manual which describes k5/k6:

https://github.com/JohnEarnest/ok/blob/gh-pages/docs/Manual....