Tried again. The USBHDD is installed as sda. There is nothing obvious to the untutored eye in the dmesg methods that describe detecting and installing sda. There seem to be no messaged from Knoppix in /var/log. But the files are simply not copied to the USBHDD with option tohd.

If tohd is known to work for USB hard drives, then I will simply write this off to hardware failure in an old computer.