/usr/include/KF5/AkonadiAgentBase/ is in libkf5akonadi-dev 4:15.12.3-0ubuntu1.
This file is owned by root:root, with mode 0o755.
..
/usr/include/KF5/AkonadiAgentBase/AgentBase
/usr/include/KF5/AkonadiAgentBase/AgentSearchInterface
/usr/include/KF5/AkonadiAgentBase/ResourceBase
/usr/include/KF5/AkonadiAgentBase/ResourceSettings
/usr/include/KF5/AkonadiAgentBase/TransportResourceBase
/usr/include/KF5/AkonadiAgentBase/agentbase.h
/usr/include/KF5/AkonadiAgentBase/agentsearchinterface.h
/usr/include/KF5/AkonadiAgentBase/akonadiagentbase_export.h
/usr/include/KF5/AkonadiAgentBase/resourcebase.h
/usr/include/KF5/AkonadiAgentBase/resourcebasesettings.h
/usr/include/KF5/AkonadiAgentBase/resourcesettings.h
/usr/include/KF5/AkonadiAgentBase/transportresourcebase.h