Your code gets up to the connection with a BLE device, but does not register for receipt of updates, nor does it attempt to read from the device.
Once the registration is done, incoming packets via the StringsReceived block (assuming strings) will be accompanied by UUIDs that you can filter by Characteristic.
See
for how to see what UUIDs are available from your device, and the data formats in the packets it sends.
(I am searching for a link to a current doc on the BLE workflow. Here's a link to the block level reference, of little help for that.)