- At https://sharplispers.github.io/clx/
- HTML, from common-lisp.net's CMUCL project
- texinfo, from http://www.emmett.ca/~sabetts/clx.texi.gz
A separate tutorial walks through some simple examples to help you get a window up quickly, so that you can study the manual in conjunction with running code.
The telent CLX tree contains a branch of the texinfo manual which has been updated in places to document new functionality as well.