On z/OS, user trace is run against a specific execution group for a broker. You can specify an extra flag on the command to trace a specific message flow.
On z/OS, service trace can be run for a specific execution group (like user trace). You can specify an extra flag on the command to trace a specific message flow.
Unlike user trace, service trace can also be run against an active agent (that is, a broker, User Name Server, or Configuration Manager).
If you specify a broker, or any of its resources (execution group or message flow), you must have deployed those resources and the component must be running before you can query trace settings.