To track a Digi Router it must have a GPS connected. In both WR41 and WR44 the GPS can be part of the router. Typically GPS is used in WR44R, which is also Vehicle Approved - see TransPort WR44 Series.
To get more information on how to set up the GPS please download the Digi TransPort User Manual and search for GPS.
GPS port must be correctly set up to get it to work. A brief note is in the attached document USB_GPS.PDF
In addition your Router must of course have a Doppler Account.