If you want the devices in a list, you can add a "Reference set selector”-widget to the Dataview showing your User-Object:
If you want the Devices concatenated in one field, then in the dataview of the User, add an “input reference set selector”-widget:
In both you will have to set the Datasource to User/User_Device/Device. You domain model has the arrow pointing from User to Device, so you will be able to select Device as your Datasource.
They look slightly different: