For each device in your app we display the current items in its inbox.
To access this page, expand the Audience menu and click in Devices like shown below:
In this page you will presented with the list of all your devices, click in the device you wish to get more information of:
In the top right corner of this page, you'll find the Options menu, here you can quickly go to the device inbox:
Then you will find all the items currently stored in this device's inbox: