In terminal
ls -ld /home/knoppix/Desktop

You should see something like this:
drwxr-xr-x 2 knoppix knoppix 4096 May 25 07:09 /home/knoppix/Desktop

DRWXR means - D - directory R-read W-write X-execute for owner
XR is read and execute for the group and for other users. If you see this it means your permissions are fine