/usr/include/KF5/KontactInterface/ is in libkf5kontactinterface-dev 16.04.2-1.
This file is owned by root:root, with mode 0o755.
..
/usr/include/KF5/KontactInterface/KontactInterface/
/usr/include/KF5/KontactInterface/KontactInterface/Core
/usr/include/KF5/KontactInterface/KontactInterface/PimUniqueApplication
/usr/include/KF5/KontactInterface/KontactInterface/Plugin
/usr/include/KF5/KontactInterface/KontactInterface/Processes
/usr/include/KF5/KontactInterface/KontactInterface/Summary
/usr/include/KF5/KontactInterface/KontactInterface/UniqueAppHandler
/usr/include/KF5/KontactInterface/kontactinterface/
/usr/include/KF5/KontactInterface/kontactinterface/core.h
/usr/include/KF5/KontactInterface/kontactinterface/kontactinterface_export.h
/usr/include/KF5/KontactInterface/kontactinterface/pimuniqueapplication.h
/usr/include/KF5/KontactInterface/kontactinterface/plugin.h
/usr/include/KF5/KontactInterface/kontactinterface/processes.h
/usr/include/KF5/KontactInterface/kontactinterface/summary.h
/usr/include/KF5/KontactInterface/kontactinterface/uniqueapphandler.h