/usr/include/KF5/SonnetUi/ is in libkf5sonnet-dev 5.28.0-2.
This file is owned by root:root, with mode 0o755.
..
/usr/include/KF5/SonnetUi/Sonnet/
/usr/include/KF5/SonnetUi/Sonnet/ConfigDialog
/usr/include/KF5/SonnetUi/Sonnet/ConfigWidget
/usr/include/KF5/SonnetUi/Sonnet/Dialog
/usr/include/KF5/SonnetUi/Sonnet/DictionaryComboBox
/usr/include/KF5/SonnetUi/Sonnet/Highlighter
/usr/include/KF5/SonnetUi/Sonnet/SpellCheckDecorator
/usr/include/KF5/SonnetUi/sonnet/
/usr/include/KF5/SonnetUi/sonnet/configdialog.h
/usr/include/KF5/SonnetUi/sonnet/configwidget.h
/usr/include/KF5/SonnetUi/sonnet/dialog.h
/usr/include/KF5/SonnetUi/sonnet/dictionarycombobox.h
/usr/include/KF5/SonnetUi/sonnet/highlighter.h
/usr/include/KF5/SonnetUi/sonnet/sonnetui_export.h
/usr/include/KF5/SonnetUi/sonnet/spellcheckdecorator.h