May want to look at the below thread. Reading your question sparked my interest but I do know know the answer: https://forums.dovetailgames.com/threads/where-are-the-donkeys.23770/ I may not be able to focus as much on learning to drive trains now knowing I could spot a donkey, LOL.
The thread linked above shows the location. You need to be aware that there is an invisible wall at Chatha preventing the camera from getting to the location of the donkey. You need to follow the instructions further down in the thread, requiring you to use the free cam from the Rochester end of the tunnel and glitch it outside the boundaries. Once done, you can free fly the cam back to Chatham to find it
