Unless your friend somehow came up with his own customized version of Knoppix, that he burned to a CD, and gave to you, there is NO ROOT PASSWORD.

For the last time: You have to SET THE ROOT PASSWORD YOURSELF.

Proof: If there already was a password set, when you issued the "sudo passwd" command, it'd ask you for the existing password before it'd let you set a new one. Does it?

Also see "README_security.txt" on the Knoppix CD (in the /KNOPPIX dir).

(And how could your friend set a password on a CD, given that CDs are a read-only medium?)