/usr/include/kadu/plugins/docking/ is in kadu-dev 3.0~rc1-1.
This file is owned by root:root, with mode 0o755.
..
/usr/include/kadu/plugins/docking/docking-configuration-provider.h
/usr/include/kadu/plugins/docking/docking-configuration.h
/usr/include/kadu/plugins/docking/docking-exports.h
/usr/include/kadu/plugins/docking/docking-menu-action-repository.h
/usr/include/kadu/plugins/docking/docking-menu-handler.h
/usr/include/kadu/plugins/docking/docking-plugin.h
/usr/include/kadu/plugins/docking/docking-tooltip-handler.h
/usr/include/kadu/plugins/docking/docking.h
/usr/include/kadu/plugins/docking/status-notifier-item-attention-animator.h
/usr/include/kadu/plugins/docking/status-notifier-item-attention-blinker.h
/usr/include/kadu/plugins/docking/status-notifier-item-attention-mode.h
/usr/include/kadu/plugins/docking/status-notifier-item-attention-static.h
/usr/include/kadu/plugins/docking/status-notifier-item-attention.h
/usr/include/kadu/plugins/docking/status-notifier-item-configuration.h
/usr/include/kadu/plugins/docking/status-notifier-item.h