Probably the simplest thing to do is talk to the programmer in charge of the process that writes the messages. I believe the CICS transaction to be started is specified somewhere in the sending program.
If that's not available, you might be able to tell by looking at the handshake between the trigger initiator transaction (CKTI) and the target CICS transaction. When CKTI kicks off the application transaction it creates a message including the queue name the target task is supposed to read. You may be able to intercept that message using a debugging tool like CEDX or forcing an ABEND that would create a dump.
This was first published in January 2008