pluginload file
The pluginload subcommand loads the plug-in specified by the file parameter. The file parameter should specify a path to the plug-in.
The pluginload subcommand can be run only while the dbx debug program is running.
pluginload /home/user/dbx_plugins/libdbx_sample.dll
See the pluginload subcommand and also the topic on developing for the dbx plug-in framework in z/OS UNIX System Services Programming Tools.