In my small application, I try to show gnome help of other gnome application, and thanks to Juhaz on GimpNet-#gnome irc channel, I learned that how the ghelp URL looks like,
gnome_url_show ("ghelp:gedit#gedit-prefs", NULL), /* #gedit-prefs is a section in the doc-book source */
or use the gnome-open utility to open it,
$ gnome-open ghelp:gedit#gedit-prefs
The nice piece is it will choose the proper ghelp file according to the running locale.