If you have connected to a device, but want to write code to discover it, you need to know the service address/guid of the bluetooth device, in order to talk to it.
On Windows if you navigate to
HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Enum\BTHENUM\
You will see the devices connected and then in HardwareID you will see the value at the end for SPP it is usually.
BTHENUM\{00001101-0000-1000-8000-00805f9b34fb}
On Windows if you navigate to
HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Enum\BTHENUM\
You will see the devices connected and then in HardwareID you will see the value at the end for SPP it is usually.
BTHENUM\{00001101-0000-1000-8000-00805f9b34fb}