/usr/include/KF5/KDESu/ is in libkf5su-dev 5.18.0-0ubuntu1.
This file is owned by root:root, with mode 0o755.
..
/usr/include/KF5/KDESu/KDESu/
/usr/include/KF5/KDESu/KDESu/Client
/usr/include/KF5/KDESu/KDESu/PtyProcess
/usr/include/KF5/KDESu/KDESu/SshProcess
/usr/include/KF5/KDESu/KDESu/StubProcess
/usr/include/KF5/KDESu/KDESu/SuProcess
/usr/include/KF5/KDESu/kdesu/
/usr/include/KF5/KDESu/kdesu/client.h
/usr/include/KF5/KDESu/kdesu/defaults.h
/usr/include/KF5/KDESu/kdesu/kdesu_export.h
/usr/include/KF5/KDESu/kdesu/process.h
/usr/include/KF5/KDESu/kdesu/ptyprocess.h
/usr/include/KF5/KDESu/kdesu/ssh.h
/usr/include/KF5/KDESu/kdesu/sshprocess.h
/usr/include/KF5/KDESu/kdesu/stub.h
/usr/include/KF5/KDESu/kdesu/stubprocess.h
/usr/include/KF5/KDESu/kdesu/su.h
/usr/include/KF5/KDESu/kdesu/suprocess.h