/usr/include/akonadi/calendar/ is in kdepimlibs5-dev 4:4.14.10-1ubuntu7.
This file is owned by root:root, with mode 0o755.
..
/usr/include/akonadi/calendar/akonadi-calendar_export.h
/usr/include/akonadi/calendar/blockalarmsattribute.h
/usr/include/akonadi/calendar/calendarbase.h
/usr/include/akonadi/calendar/calendarclipboard.h
/usr/include/akonadi/calendar/calendarsettings.h
/usr/include/akonadi/calendar/etmcalendar.h
/usr/include/akonadi/calendar/fetchjobcalendar.h
/usr/include/akonadi/calendar/freebusymanager.h
/usr/include/akonadi/calendar/freebusyproviderbase.h
/usr/include/akonadi/calendar/history.h
/usr/include/akonadi/calendar/icalimporter.h
/usr/include/akonadi/calendar/incidencechanger.h
/usr/include/akonadi/calendar/itiphandler.h
/usr/include/akonadi/calendar/publishdialog.h
/usr/include/akonadi/calendar/standardcalendaractionmanager.h
/usr/include/akonadi/calendar/todopurger.h