plugin[name[command]]
The plugin subcommand passes the command specified by the command parameter to the plug-in specified by the name parameter. If no parameters are specified, the names of all available plug-ins are displayed.
The plugin subcommand can be run only while the dbx debug program is running.
plugin
plugin sample help
plugin xyz interpret 0x12345678
See the pluginload subcommand and also the topic on Developing for dbx Plug-in Framework in z/OS UNIX System Services Programming Tools.