/usr/bin/HelpViewer is in helpviewer.app 0.3-8+b3.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/bin/../lib/GNUstep/Applications/HelpViewer.app/HelpViewer
/usr/bin/../lib/GNUstep/Applications/HelpViewer.app/HelpViewer