/usr/include/gnome-todo/ is in libgnome-todo-dev 3.28.1-1.
This file is owned by root:root, with mode 0o755.
..
/usr/include/gnome-todo/gnome-todo.h
/usr/include/gnome-todo/gtd-activatable.h
/usr/include/gnome-todo/gtd-enums.h
/usr/include/gnome-todo/gtd-manager.h
/usr/include/gnome-todo/gtd-notification.h
/usr/include/gnome-todo/gtd-object.h
/usr/include/gnome-todo/gtd-panel.h
/usr/include/gnome-todo/gtd-provider.h
/usr/include/gnome-todo/gtd-task-list-view.h
/usr/include/gnome-todo/gtd-task-list.h
/usr/include/gnome-todo/gtd-task.h
/usr/include/gnome-todo/gtd-timer.h
/usr/include/gnome-todo/gtd-types.h
/usr/include/gnome-todo/gtd-utils.h
/usr/include/gnome-todo/gtd-window.h