First, type

lsmod

to see if the correct modules are loaded. At a minimum, you need the OHCI driver module to be loaded up and appear on the list.

Assuming that knoppix has not changed much, you can also view your usb information graphically by typing

usbview

Maybe you can get the information this way. But if you cannot even see the USB host controller, you definitely won't be able to see the serial device.