You want to debug the server job that one of RJS Software's client products is using. But you don't know what the job will be, since host server jobs often end after the client is finished.
Use Service Entry Points (SEPs).
This feature is available on the iSeries in V5R2 or higher. When you use an SEP, you don't need to know what job will be running your program. This is especially useful for debugging exit programs that run in host server jobs, because these jobs often do not exist until needed.
There are several articles that explain how to use SEPs: