Trace in enabled with a registry key, HKEY_LOCAL_MACHINE\SOFTWARE\IBM\MQe\CurrentVersion\Trace.
All values are of type REG_SZ. The is the following two values are the minimum required for trace to be produced:
Enable=Yes Location=c:\my\directory\structure\mqetrace
Where enable turns trace on and the location is the directory in which trace files are produced. This directory is created if it does not exist already.
In addition to these required values, there are a number of optional entries that affect the output trace.