KDE is one of the two major desktop environments available on linux, the other one being gnome. KDE is the one included with knoppix. I just checked, and can confirm that xmag is on the CD, and kmag and xzoom are available as debian packages and can thusly be installed using apt-get. That is, if your knoppix has been installed to hard disk. To give xmag a try, simply type "xmag" from a console or from the <Alt><F2> prompt.