uhm, manually mounting the disk? should not be needed, but if you want to try... type
Code:
sudo su&&mkdir /mnt/device&&mount -t filesystem /dev/device /mnt/device&&exit
where filesystem is replaced with either vfat, ntfs, or whatever you have on that disk (USB pendrive is most likely vfat) if you had linux on that disk beofre possibly, reiserfs, ext2, ext3, JFS and many more.

device is replaced with the device "name" it gets when plugged in, leave it unplugged and when knoppix is fully booted open a console and type
Code:
dmesg
now note what the last 10-15 lines read, plug in the disk wait a few min open a new console next to the one you just opened and type dmesg, there should now be lines there not present in the first window. you should see something like this.
scsi 5:0:0:0: Direct-Access SigmaTel MSCN 0100 PQ: 0 ANSI: 4
sd 5:0:0:0: [sdb] 487936 2048-byte hardware sectors (999 MB)
sd 5:0:0:0: [sdb] Write Protect is off
sd 5:0:0:0: [sdb] Mode Sense: 3e 00 00 00
sd 5:0:0:0: [sdb] Assuming drive cache: write through
sd 5:0:0:0: [sdb] 487936 2048-byte hardware sectors (999 MB)
sd 5:0:0:0: [sdb] Write Protect is off
sd 5:0:0:0: [sdb] Mode Sense: 3e 00 00 00
sd 5:0:0:0: [sdb] Assuming drive cache: write through
sdb: sdb1
sd 5:0:0:0: [sdb] Attached SCSI removable disk
sd 5:0:0:0: Attached scsi generic sg1 type 0
usb-storage: device scan complete
in this case sdb1 is what I would type as disk name.

keep asking.