/usr/include/hkl/ is in libhkl-dev 4.0.3-4ubuntu1.
This file is owned by root:root, with mode 0o755.
..
/usr/include/hkl/hkl-axis.h
/usr/include/hkl/hkl-detector-factory.h
/usr/include/hkl/hkl-detector.h
/usr/include/hkl/hkl-error.h
/usr/include/hkl/hkl-geometry-factory.h
/usr/include/hkl/hkl-geometry.h
/usr/include/hkl/hkl-interval.h
/usr/include/hkl/hkl-lattice.h
/usr/include/hkl/hkl-list.h
/usr/include/hkl/hkl-macros.h
/usr/include/hkl/hkl-matrix.h
/usr/include/hkl/hkl-parameter.h
/usr/include/hkl/hkl-pseudoaxis-auto.h
/usr/include/hkl/hkl-pseudoaxis-common-eulerians.h
/usr/include/hkl/hkl-pseudoaxis-common-hkl.h
/usr/include/hkl/hkl-pseudoaxis-common-psi.h
/usr/include/hkl/hkl-pseudoaxis-common-q.h
/usr/include/hkl/hkl-pseudoaxis-common.h
/usr/include/hkl/hkl-pseudoaxis-e4cv.h
/usr/include/hkl/hkl-pseudoaxis-e6c.h
/usr/include/hkl/hkl-pseudoaxis-factory.h
/usr/include/hkl/hkl-pseudoaxis-k4cv.h
/usr/include/hkl/hkl-pseudoaxis-k6c.h
/usr/include/hkl/hkl-pseudoaxis-zaxis.h
/usr/include/hkl/hkl-pseudoaxis.h
/usr/include/hkl/hkl-quaternion.h
/usr/include/hkl/hkl-sample.h
/usr/include/hkl/hkl-source.h
/usr/include/hkl/hkl-unit.h
/usr/include/hkl/hkl-vector.h