I would like to know in iOS9 split-screen mode, whether my own App is in the main app position or vice app position.
Main app position or vice app position
That information is (by design) not available. What are you trying to do?
I want to make two apps interact in split view mode on iOS9, for example, you can drag an icon from left screen app to the right screen app, and I also want to know whether current app is in the main app position or vice app position.
That makes sense, but the SDK does not allow for that. Neither application can draw over the other, and there isn't much in the way of IPC to enable them to easily communicate between each other either.