Not sure what you're trying to do, but simply mounting the image was IIRC:
Code:
insmod cloop file=/cdrom/KNOPPIX/KNOPPIX
mount -r -o loop /dev/cloop /mountpoint
I may forget something (I am not running knoppix now), but this is explained in a presentation availbale on the knopper site. That document is in German but the slides still help. Also I think cloop v2 allows mounting of several compressed images, but I don't know what the syntax would be in that case.