If you are writing application-specific help, there are two ways to ensure that your application has help on help for its own help dialogs:
Rely on the desktop's help on help volume. For example, on workstations running the desktop, the standard Help4Help volume is installed.
Supply your own help on help volume. The HelpTag source files for the Help4Help volume are provided in the /usr/dt/dthelp/help4help/C directory. A control subdirectory contains HelpTag processing files. You run HelpTag in this directory to create the run-time help file. Graphics files used in the help on help volume are stored in the control/graphics subdirectory.