Problem:
QLOG() provides some more detailed information of the new query optimizer. This info may be for debug/development only, but there may be important details that Support could use in customer cases.

It appears that this setting can only be set at Startup and not Runtime

qlog.cpp: 35 MONGO_EXPORT_SERVER_PARAMETER(verboseQueryLogging, bool, false);

The last boolean controls CHANGE_AT_RUNTIME

Solution:
Change QLOG so that CHANGE_AT_RUNTIME=True

Workaround:
Shutdown/Startup the mongod to set the parameter - but you loose context of the current kernel state, cached blocks etc.