As Traktor is not supported by Automap, the 'learn' button on the Nocturn will not learn parameters in Traktor. You'll need to create a Midi Client and use Traktor's own learn system to assign parameters to control.

Make sure you are using the latest version of Automap and Traktor.

To create a Midi Client, set the MIDI input and output ports for the Automap MIDI Client to 'Automap MIDI' in the Automap settings menu.

Activate MIDI channel(s) from the Automap settings menu and select the newly added MIDI control map from the Browser View of the Automap Universal window by pressing the 'User' button.

In Traktor Preferences > Hotkey & Midi Setup > Midi Interfaces, make sure the 'Automap Midi' is active for the midi in and midi out ports. A cross next to it denotes that is active.

Then go to Preferences > Hotkey & Midi Setup > Midi Setup, click 'Add', then select a parameter. Click the 'Learn' button in Traktor and move a control on the Nocturn. Press 'Learn' again in Traktor when you finished learning. You can freely adjust the settings in that page according to your own preferences.

You can also rename parameter names on the Nocturn GUI as well.