it creates a compressed file in /mnt/knx/NewCD/KNOPPIX, perhaps you didn't see it ?

Then you do:

mkisofs -pad -l -r -J -v -V -joliet-long -b boot/isolinux/isolinux.bin -no-emul-boot -boot-load-size 4 -boot-info-table -c KNOPPIX/boot.cat -hide-rr-moved -o /.../myknoppix.iso /mnt/knx/NewCD

which creates the iso-file to burn on cd. You can test it with

qemu -m 128 -cdrom /.../myknoppix.iso -boot d -user-net

bye
Klaus