Alexa Device Capabilities Report
Dashbot has a powerful Device Capabilities Report that will tell you how many of your users are accessing your skill with a display capable device.
In order to see data for this, however, you must enable the Display Interface for your skill prior to submission to Amazon.
In order to do this, go to your Alexa Developer Console, and under the “Interfaces” menu, turn on the “Display Interface” selection
Once this is enabled, you will see a Device Capability report that looks like this: