In the kde-frameworks/kdesu package, there is no kdesu executable (surprisingly). It can be found in kde-plasma/kde-cli-tools, it is in /usr/lib64/libexec/kf5/kdesu. However, that's not in the path, so I can't execute kdesu from a konsole or from krunner.
/usr/lib64/libexec -> http://www.linuxbase.org/betaspecs/fhs/fhs/ch04s07.html