Its command is k3b. If it says its not found, make sure it is in your $PATH. Type
and see where is tells you it is. They type
and make sure the k3b location is listed as part of your path. If the k3b is not in your path, you will need to type the entire location, such as /usr/bin/k3b as it is on my system. If whereis doesn't return anything the k3b is probably not installed.