First, you will want to make sure that you are sending a MIDI message to Traktor.  You will see the CTRL light on the top of the Traktor interface.  This will light up if you are sending a MIDI signal into Traktor.  If this lights up, that means you can then send that MIDI signal to Traktor.
If you are getting the signal in, you will then want to go to the the Controller Manager screen in the Preferences menu.
From here you will want to select your device.  You will want to select Add, and then you can then either load the DDM4000 template or make your own mappings.  If you choose to use the DDM4000 mapping, it can be found by selecting IMPORT then Settings/Default Settings/Controller/Behringer/Controller - Behringer - DDM4000.tsi.
When you have this loaded, you can make your own changes and modifications by selecting the 'Add In' button.  After selecting 'Add In', you can then modify the control to reflect the way you would like it to perform by changing the 'mapping details.'