/usr/include/KF5/Syndication/syndication/atom/ is in libkf5syndication-dev 16.04.2-1.
This file is owned by root:root, with mode 0o755.
..
/usr/include/KF5/Syndication/syndication/atom/atom.h
/usr/include/KF5/Syndication/syndication/atom/category.h
/usr/include/KF5/Syndication/syndication/atom/constants.h
/usr/include/KF5/Syndication/syndication/atom/content.h
/usr/include/KF5/Syndication/syndication/atom/document.h
/usr/include/KF5/Syndication/syndication/atom/entry.h
/usr/include/KF5/Syndication/syndication/atom/generator.h
/usr/include/KF5/Syndication/syndication/atom/link.h
/usr/include/KF5/Syndication/syndication/atom/parser.h
/usr/include/KF5/Syndication/syndication/atom/person.h
/usr/include/KF5/Syndication/syndication/atom/source.h