Majority of the reverse engineering started with packet inspection and reversing the APK's from the Android version. From there a lot of effort was put in to protobuf's and reversing the protobuf messages. Two things learned from the packet inspection was the authentication schemes for Pokemon Trainer Club and Google; and then how to use the JWT's in the API requests. All of the protobuf requests have been figured out, but sometimes it's about implementation details in how things are called (for example S2 cellid's for map object requests, etc).