/usr/include/osgViewer/ is in libopenscenegraph-dev 3.2.3+dfsg1-2ubuntu8.
This file is owned by root:root, with mode 0o755.
..
/usr/include/osgViewer/CompositeViewer
/usr/include/osgViewer/Export
/usr/include/osgViewer/GraphicsWindow
/usr/include/osgViewer/Keystone
/usr/include/osgViewer/Renderer
/usr/include/osgViewer/Scene
/usr/include/osgViewer/Version
/usr/include/osgViewer/View
/usr/include/osgViewer/Viewer
/usr/include/osgViewer/ViewerBase
/usr/include/osgViewer/ViewerEventHandlers
/usr/include/osgViewer/api/
/usr/include/osgViewer/api/X11/
/usr/include/osgViewer/api/X11/GraphicsHandleX11
/usr/include/osgViewer/api/X11/GraphicsWindowX11
/usr/include/osgViewer/api/X11/PixelBufferX11