/usr/include/KF5/Akonadi/ is in libkf5akonadicalendar-dev 4:17.12.3-0ubuntu1.
This file is owned by root:root, with mode 0o755.
..
/usr/include/KF5/Akonadi/Calendar/
/usr/include/KF5/Akonadi/Calendar/BlockAlarmsAttribute
/usr/include/KF5/Akonadi/Calendar/CalendarBase
/usr/include/KF5/Akonadi/Calendar/CalendarClipboard
/usr/include/KF5/Akonadi/Calendar/ETMCalendar
/usr/include/KF5/Akonadi/Calendar/FetchJobCalendar
/usr/include/KF5/Akonadi/Calendar/FreeBusyManager
/usr/include/KF5/Akonadi/Calendar/FreeBusyProviderBase
/usr/include/KF5/Akonadi/Calendar/History
/usr/include/KF5/Akonadi/Calendar/ICalImporter
/usr/include/KF5/Akonadi/Calendar/ITIPHandler
/usr/include/KF5/Akonadi/Calendar/IncidenceChanger
/usr/include/KF5/Akonadi/Calendar/PublishDialog
/usr/include/KF5/Akonadi/Calendar/StandardCalendarActionManager
/usr/include/KF5/Akonadi/Calendar/TodoPurger