/usr/include/ql/experimental/volatility/ is in libquantlib0-dev 1.9.1-1.
This file is owned by root:root, with mode 0o755.
..
/usr/include/ql/experimental/volatility/abcdatmvolcurve.hpp
/usr/include/ql/experimental/volatility/all.hpp
/usr/include/ql/experimental/volatility/blackatmvolcurve.hpp
/usr/include/ql/experimental/volatility/blackvolsurface.hpp
/usr/include/ql/experimental/volatility/equityfxvolsurface.hpp
/usr/include/ql/experimental/volatility/extendedblackvariancecurve.hpp
/usr/include/ql/experimental/volatility/extendedblackvariancesurface.hpp
/usr/include/ql/experimental/volatility/interestratevolsurface.hpp
/usr/include/ql/experimental/volatility/noarbsabr.hpp
/usr/include/ql/experimental/volatility/noarbsabrinterpolatedsmilesection.hpp
/usr/include/ql/experimental/volatility/noarbsabrinterpolation.hpp
/usr/include/ql/experimental/volatility/noarbsabrsmilesection.hpp
/usr/include/ql/experimental/volatility/sabrvolsurface.hpp
/usr/include/ql/experimental/volatility/sviinterpolatedsmilesection.hpp
/usr/include/ql/experimental/volatility/sviinterpolation.hpp
/usr/include/ql/experimental/volatility/svismilesection.hpp
/usr/include/ql/experimental/volatility/swaptionvolcube1a.hpp
/usr/include/ql/experimental/volatility/volcube.hpp
/usr/include/ql/experimental/volatility/zabr.hpp
/usr/include/ql/experimental/volatility/zabrinterpolatedsmilesection.hpp
/usr/include/ql/experimental/volatility/zabrinterpolation.hpp
/usr/include/ql/experimental/volatility/zabrsmilesection.hpp