I don't have much experience on Knoppix.
But all you have to do is open a terminal app. And as root or admin user you have to type commands as I posted.
But before typing the said commands in terminal app run 'dmesg | tail -n 20' both before and after inserting a cf card. You will have interpret it and some where it would show the device as /dev/sdx or something similar (may be hdx or ubx). Do same after pluging second cf card. And CAREFUL don't put source card and destination card device files in reverse else you will loss all the content/data of card you want to copy.
Better is you make a backup of source card and then proceed. So to do that:
dd if=/dev/sdx of=backupfile.img