When it is iBeacon, all data is in “Manufacturer Specific Data” of the advertisement. Any library you use will be able to access these bytes. Often first two bytes for the manufacturer itself, rest for the data. You have two tasks, extracting the data and understanding it.

To understand it, monitor existing iBeacons and look at the manufacturer data with a scanner tool like github.com/RT-circuits/ble-tools.

If you “see” the mfg data in tools like that (use the advanced scanner for hex/ascii output), look at the Python code to see how it is “extracted” from the advertisement. It is all relatively straightforward (at the end).