You don't tell us which release of Knoppix you are using, but *assuming* that it is 5.1.x or 5.0.x your /etc/apt/sources.list file if unmodified will be using obsolete designations of what "stable" "testing" and "unstable" mean for Debian packages.
I recommend that you read up about packaging on http://www.debian.org/distrib/packages
but anyway try invoking
Code:
apt-get update
apt-get -s install evolution
and assess whether you are happy with what the apt-get simulation tells you it will install|upgrade|remove if applicable.
If you want to proceed then
Code:
apt-get install evolution
will probably work for you.