/usr/include/KF5/akonadi/ is in libkf5akonadicontact-dev 4:17.12.3-0ubuntu1.
This file is owned by root:root, with mode 0o755.
..
/usr/include/KF5/akonadi/contact/
/usr/include/KF5/akonadi/contact/abstractcontactformatter.h
/usr/include/KF5/akonadi/contact/abstractcontactgroupformatter.h
/usr/include/KF5/akonadi/contact/akonadi-contact_export.h
/usr/include/KF5/akonadi/contact/contactdefaultactions.h
/usr/include/KF5/akonadi/contact/contacteditor.h
/usr/include/KF5/akonadi/contact/contacteditordialog.h
/usr/include/KF5/akonadi/contact/contactgroupeditor.h
/usr/include/KF5/akonadi/contact/contactgroupeditordialog.h
/usr/include/KF5/akonadi/contact/contactgroupexpandjob.h
/usr/include/KF5/akonadi/contact/contactgroupsearchjob.h
/usr/include/KF5/akonadi/contact/contactgroupviewer.h
/usr/include/KF5/akonadi/contact/contactgroupviewerdialog.h
/usr/include/KF5/akonadi/contact/contactparts.h
/usr/include/KF5/akonadi/contact/contactsearchjob.h
/usr/include/KF5/akonadi/contact/contactsfilterproxymodel.h
/usr/include/KF5/akonadi/contact/contactstreemodel.h
/usr/include/KF5/akonadi/contact/contactviewer.h
/usr/include/KF5/akonadi/contact/contactviewerdialog.h
/usr/include/KF5/akonadi/contact/emailaddressrequester.h
/usr/include/KF5/akonadi/contact/emailaddressselection.h
/usr/include/KF5/akonadi/contact/emailaddressselectiondialog.h
/usr/include/KF5/akonadi/contact/emailaddressselectionmodel.h
/usr/include/KF5/akonadi/contact/emailaddressselectionwidget.h
/usr/include/KF5/akonadi/contact/selectaddressbookdialog.h
/usr/include/KF5/akonadi/contact/standardcontactactionmanager.h
/usr/include/KF5/akonadi/contact/standardcontactformatter.h
/usr/include/KF5/akonadi/contact/standardcontactgroupformatter.h