Take a look at this table that @Wildtypitch (kudos once again) had made earlier.
So I guess you can use -C /dev/ttyAMA0 switch for Vue Pro as it expects 57600 baudrate Mavlink stream.
/dev/ttyAMA0 corresponds to a port soldered out on Navio 2 and named UART.
In order to use a radio for telemetry you’d need an additional UART (i.g. FT232 or CP2102 will do). After you hook up one, this will be identified as /dev/ttyUSB0.
To sum up, this will be something like -C /dev/ttyAMA0 -D /dev/ttyUSB0.
You can also use Wi-Fi for telemetry. This is way easier:
-A udp:<GCS_IP>:<PORT> -C /dev/ttyAMA0.
I hope, it’s clearer now.