Look at some of the source files used by UNIXhelp as you read through the Deskhelp documentation. These can be found in the directory(ies) specified by the variable XDH_TOPIC_PATH. For example:
echo $XDH_TOPIC_PATH /usr/local/lib/helpdata:/usr/local/lib/helpdata/manpages
This displays the pathname(s) for the directories.