At the moment, communicating back from the MobileTogether solution is possible only by writing files in solution’s local storage or in any other accessible directory (Music, Videos, Pictures).
SolutionView control provides access to solution’s local storage via method mySolutionView.GetSolutionLocalFolder().
How solution communicates with server depends how you designed a solution (in MT Designer). If 3rd party app sends embedded message to SoltuionView via ProcessEmbeddedMessageAsync() method, solution processes OnEmbeddedMessage page event. In that event you can do whatever you want ( by designing actions tree in MT designer ).
If you send message back from the solution (via action ‘Send Embedded Message Back’), SolutionView control will fire event EmbeddedMessage, and if you sync it in your UWP app, you can listen what solution sends (search in attached MainPage.xaml.cpp file SolutionViewRight_EmbeddedMessage and SolutionViewLeft_EmbeddedMessage).
In the MT embedding demo, the bottom field allows opening a solution in a new window. How does this new window connect to the server?
Each SolutionView control is a world for itself. You can have 10 of them in your app, but they do not interfere each other, and it is irrelevant if they are in the same or new window. The parameters for communication I pick up from the main page and propagate them to that new window (named PopupSolutionPage). How the page is created and parameters passed, search for MtSolutionInNewWindowRun_Click() in MainPage.xaml.cpp