There have been bug report pages in the Wiki for earlier releases of Knoppix, but none for 6+. So, just having come across a small hardware detection bug today, I created 6.4.4-pages and entered a few known issues.

There are links on the main bug page, http://www.knoppix.net/w/index.php?title=Bugs. Following the tradition, there are separate bug pages for CD and DVD:
DVD: http://www.knoppix.net/wiki/Bugs/6.4.4DVD
CD: http://www.knoppix.net/wiki/Bugs/6.4.4CD

Don't double-post for something that affects both, it isn't necessary. You might also want to check out the knoppix-devel mailing list to see if it has been handled already: http://lists.debian.org/debian-knoppix/2011/

As for 6.5, I don't intend to do anything, as very few of us seem to use it, and I rather wait for the next release myself. But of course 6.5 bug pages also belong there.