... if you are using an up-to-date Knoppix (Knoppix 6.4.4) then the filemanager is the PCManFM.
The only place I can see it is in the partition manager. It has a black square next to it and under the type column, it says "unknown".
In this case you can try to restore some thing with "TestDisk" (on the Knoppix CD).

Be aware, it is a dangerous tool, not for beginners! Read all the documentations at the authors side

http://www.cgsecurity.org/wiki/TestDisk


Greetings Werner * http://www.wp-schulz.de/knoppix/summary.html
Own Rescue-CD with Knoppix (Knoppix V6.4.4 remaster)