/usr/include/KF5/KNotifications/ is in libkf5notifications-dev 5.18.0-0ubuntu1.
This file is owned by root:root, with mode 0o755.
..
/usr/include/KF5/KNotifications/KNotification
/usr/include/KF5/KNotifications/KNotificationPlugin
/usr/include/KF5/KNotifications/KNotificationRestrictions
/usr/include/KF5/KNotifications/KNotifyConfig
/usr/include/KF5/KNotifications/KPassivePopup
/usr/include/KF5/KNotifications/KStatusNotifierItem
/usr/include/KF5/KNotifications/knotification.h
/usr/include/KF5/KNotifications/knotificationplugin.h
/usr/include/KF5/KNotifications/knotificationrestrictions.h
/usr/include/KF5/KNotifications/knotifications_export.h
/usr/include/KF5/KNotifications/knotifyconfig.h
/usr/include/KF5/KNotifications/kpassivepopup.h
/usr/include/KF5/KNotifications/kstatusnotifieritem.h