To turn on just right click on your project and go to project properties (do it on View Controller project if you are debugging for a UI flow) and go to run/debug/profile. Choose the default profile and click edit. You will java option and a text box near to it.
In the text box add -Djbo.debugoutput=console. Add it separated by a space if there is something already.
Now bounce the WLS (weblogic server) and re-run the app. You will see the app printing low level messages in the jdev log window. You must take care to turn it off by either removing the above stmt or changing it to: -Djbo.debugoutput=silent in case of production environment. This will run significantly slow otherwise. It's also a better idea to keep it off in development environment when not needed.