The big block (Fibocom L816-AM) appears to be a LTE module. But the product information was somehow removed from the company's website (although still viewable through Google Cache).
User Manual:
https://fccid.io/ZMOL816AM/Users-Man...al-3156027.pdf
It would be interesting to see if the WiFi only model have this module or not.
With my limited knowledge in circuits, here's my guess:
I'm seeing three antenna sockets on the top, supposedly 2 (on the left) for the LTE module and one (one the right) for Bluetooth. Then there is the connector for the display at the bottom center? I'm also not sure about the 3 connectors on the right, maybe one for the touch screen, one for the USB port and one for the battery or hardware button? It would be better if OP can upload photo for the other disassembled parts.
The pins numbered 1-5 might be worth looking into.