UPDATE:
From their own site:
The steps for installing the Nokia X packages with the SDK Manager are the following:
Open the SDK Manager and select Tools -> Manage Add-on Sites...
Open User Defined Sites tab and click the New... button
Enter the following URL to the Add Add-on Site URL dialog:
http://tools.nokia.com/nokia-x/repository/addon.xml
Copy code
Click OK
Click the Close button to close the Add-on Sites window
Then you need will be able to see their addon package, install it in SDK manager and see Nokia USB driver in /extras/
WINDOWS
Edit the file C:\Users\.android\adb_usb.ini and add line:
0x0421
then restart adb server.
Enabling USB debugging
In order for the ADB tool to recognise your device, you need to enable the USB debugging on the device by following these simple steps:
Launch device settings.
Tap Developer options in the System section.
Switch on developer options and tap OK in the query dialog shown.
Enable USB debugging in the Debugging section and tap OK in the query dialog shown.
Your device has now USB debugging enabled.