/usr/include/gwyddion/libprocess/ is in libgwyddion20-dev 2.38-2.
This file is owned by root:root, with mode 0o755.
..
/usr/include/gwyddion/libprocess/arithmetic.h
/usr/include/gwyddion/libprocess/brick.h
/usr/include/gwyddion/libprocess/cdline.h
/usr/include/gwyddion/libprocess/correct.h
/usr/include/gwyddion/libprocess/correlation.h
/usr/include/gwyddion/libprocess/cwt.h
/usr/include/gwyddion/libprocess/datafield.h
/usr/include/gwyddion/libprocess/dataline.h
/usr/include/gwyddion/libprocess/dwt.h
/usr/include/gwyddion/libprocess/elliptic.h
/usr/include/gwyddion/libprocess/filters.h
/usr/include/gwyddion/libprocess/fractals.h
/usr/include/gwyddion/libprocess/grains.h
/usr/include/gwyddion/libprocess/gwycaldata.h
/usr/include/gwyddion/libprocess/gwycalibration.h
/usr/include/gwyddion/libprocess/gwygrainvalue.h
/usr/include/gwyddion/libprocess/gwyprocess.h
/usr/include/gwyddion/libprocess/gwyprocessenums.h
/usr/include/gwyddion/libprocess/gwyprocesstypes.h
/usr/include/gwyddion/libprocess/hough.h
/usr/include/gwyddion/libprocess/interpolation.h
/usr/include/gwyddion/libprocess/inttrans.h
/usr/include/gwyddion/libprocess/level.h
/usr/include/gwyddion/libprocess/linestats.h
/usr/include/gwyddion/libprocess/simplefft.h
/usr/include/gwyddion/libprocess/spectra.h
/usr/include/gwyddion/libprocess/stats.h
/usr/include/gwyddion/libprocess/stats_uncertainty.h
/usr/include/gwyddion/libprocess/tip.h
/usr/include/gwyddion/libprocess/triangulation.h