/usr/include/KF5/AkonadiWidgets/ is in libkf5akonadi-dev 4:15.12.3-0ubuntu1.
This file is owned by root:root, with mode 0o755.
..
/usr/include/KF5/AkonadiWidgets/AgentActionManager
/usr/include/KF5/AkonadiWidgets/AgentInstanceWidget
/usr/include/KF5/AkonadiWidgets/AgentTypeDialog
/usr/include/KF5/AkonadiWidgets/AgentTypeWidget
/usr/include/KF5/AkonadiWidgets/CollectionComboBox
/usr/include/KF5/AkonadiWidgets/CollectionDialog
/usr/include/KF5/AkonadiWidgets/CollectionPropertiesDialog
/usr/include/KF5/AkonadiWidgets/CollectionPropertiesPage
/usr/include/KF5/AkonadiWidgets/CollectionRequester
/usr/include/KF5/AkonadiWidgets/CollectionStatisticsDelegate
/usr/include/KF5/AkonadiWidgets/CollectionView
/usr/include/KF5/AkonadiWidgets/ControlGui
/usr/include/KF5/AkonadiWidgets/ETMViewStateSaver
/usr/include/KF5/AkonadiWidgets/EntityListView
/usr/include/KF5/AkonadiWidgets/EntityTreeView
/usr/include/KF5/AkonadiWidgets/ItemView
/usr/include/KF5/AkonadiWidgets/ManageAccountWidget
/usr/include/KF5/AkonadiWidgets/RenameFavoriteDialog
/usr/include/KF5/AkonadiWidgets/StandardActionManager
/usr/include/KF5/AkonadiWidgets/SubscriptionDialog
/usr/include/KF5/AkonadiWidgets/TagEditWidget
/usr/include/KF5/AkonadiWidgets/TagManagementDialog
/usr/include/KF5/AkonadiWidgets/TagSelectWidget
/usr/include/KF5/AkonadiWidgets/TagSelectionDialog
/usr/include/KF5/AkonadiWidgets/TagWidget
/usr/include/KF5/AkonadiWidgets/agentactionmanager.h
/usr/include/KF5/AkonadiWidgets/agentinstancewidget.h
/usr/include/KF5/AkonadiWidgets/agenttypedialog.h
/usr/include/KF5/AkonadiWidgets/agenttypewidget.h
/usr/include/KF5/AkonadiWidgets/akonadiwidgets_export.h
/usr/include/KF5/AkonadiWidgets/collectioncombobox.h
/usr/include/KF5/AkonadiWidgets/collectiondialog.h
/usr/include/KF5/AkonadiWidgets/collectionpropertiesdialog.h
/usr/include/KF5/AkonadiWidgets/collectionpropertiespage.h
/usr/include/KF5/AkonadiWidgets/collectionrequester.h
/usr/include/KF5/AkonadiWidgets/collectionstatisticsdelegate.h
/usr/include/KF5/AkonadiWidgets/collectionview.h
/usr/include/KF5/AkonadiWidgets/controlgui.h
/usr/include/KF5/AkonadiWidgets/entitylistview.h
/usr/include/KF5/AkonadiWidgets/entitytreeview.h
/usr/include/KF5/AkonadiWidgets/etmviewstatesaver.h
/usr/include/KF5/AkonadiWidgets/itemview.h
/usr/include/KF5/AkonadiWidgets/manageaccountwidget.h
/usr/include/KF5/AkonadiWidgets/renamefavoritedialog.h
/usr/include/KF5/AkonadiWidgets/standardactionmanager.h
/usr/include/KF5/AkonadiWidgets/subscriptiondialog.h
/usr/include/KF5/AkonadiWidgets/tageditwidget.h
/usr/include/KF5/AkonadiWidgets/tagmanagementdialog.h
/usr/include/KF5/AkonadiWidgets/tagselectiondialog.h
/usr/include/KF5/AkonadiWidgets/tagselectwidget.h
/usr/include/KF5/AkonadiWidgets/tagwidget.h