If you really need to see what happens to a MQ message after DevTest has handed it off to the IBM code, you can add the following to the relevant vmoptions file (only for debugging - I would suggest removing as soon as possible afterwards)
-Dcom.ibm.msg.client.commonservices.trace.status=ON
-Dcom.ibm.msg.client.commonservices.trace.outputName=/tmp/mqjms_%PID%.log
-Dcom.ibm.msg.client.commonservices.trace.parameter=TRUE
-Dcom.ibm.msg.client.commonservices.trace.level=8
Change the outputName to a format and location suitable to your environment