Hi,
you can determine the connection type by checking the ADLDisplayInfo structure. The structure contains the iDisplayConnector element. This element indicates if a DP, DVI-I, DVI-D etc connection is used. Unfortunately you cannot determine the type of dongle. A display connected via active dongle looks like a DP connection and this is waht the iDisplayConnector would return in this case. For a passive dongle iDisplayConnector would be DVI-D.
Chris