uhm, first what version of knopix?

second, have you tried checking the /media/ directory? there might be something under there called sda1 or hda1(sd= scsi or Sata hd=ata) possibly sdb1 or hdb1 (a=first disk b=second d=third...) or some other number, depending on how manu partitions you have.
by the way in this regard "disk" is also SD-card, pendrive, CD, DVD or other readable media.

third, do you see any error messages during boot?

fourth, what does the comman fdisk -l (lower case L)(type in a terminal window) say, that is type
Code:
 fdisk -l
and hit enter, terminal can be called xterm aterm, Konsole and several other things.

keep asking