/usr/include/ql/termstructures/volatility/equityfx/ is in libquantlib0-dev 1.9.1-1.
This file is owned by root:root, with mode 0o755.
..
/usr/include/ql/termstructures/volatility/equityfx/all.hpp
/usr/include/ql/termstructures/volatility/equityfx/blackconstantvol.hpp
/usr/include/ql/termstructures/volatility/equityfx/blackvariancecurve.hpp
/usr/include/ql/termstructures/volatility/equityfx/blackvariancesurface.hpp
/usr/include/ql/termstructures/volatility/equityfx/blackvoltermstructure.hpp
/usr/include/ql/termstructures/volatility/equityfx/fixedlocalvolsurface.hpp
/usr/include/ql/termstructures/volatility/equityfx/gridmodellocalvolsurface.hpp
/usr/include/ql/termstructures/volatility/equityfx/hestonblackvolsurface.hpp
/usr/include/ql/termstructures/volatility/equityfx/impliedvoltermstructure.hpp
/usr/include/ql/termstructures/volatility/equityfx/localconstantvol.hpp
/usr/include/ql/termstructures/volatility/equityfx/localvolcurve.hpp
/usr/include/ql/termstructures/volatility/equityfx/localvolsurface.hpp
/usr/include/ql/termstructures/volatility/equityfx/localvoltermstructure.hpp
/usr/include/ql/termstructures/volatility/equityfx/noexceptlocalvolsurface.hpp