/usr/include/libmatewnck/ is in libmatewnck-dev 1.6.1-3.
This file is owned by root:root, with mode 0o755.
..
/usr/include/libmatewnck/libmatewnck/
/usr/include/libmatewnck/libmatewnck/application.h
/usr/include/libmatewnck/libmatewnck/class-group.h
/usr/include/libmatewnck/libmatewnck/libmatewnck.h
/usr/include/libmatewnck/libmatewnck/matewnck-enum-types.h
/usr/include/libmatewnck/libmatewnck/pager.h
/usr/include/libmatewnck/libmatewnck/screen.h
/usr/include/libmatewnck/libmatewnck/selector.h
/usr/include/libmatewnck/libmatewnck/tasklist.h
/usr/include/libmatewnck/libmatewnck/util.h
/usr/include/libmatewnck/libmatewnck/version.h
/usr/include/libmatewnck/libmatewnck/window-action-menu.h
/usr/include/libmatewnck/libmatewnck/window.h
/usr/include/libmatewnck/libmatewnck/workspace.h