Without looking at either myself, the two things I have for the yoke buttons are:
The Bonanza also has some buttons on the yoke and I'm pretty sure I saw them listed out in the manual. Or maybe it was looking at Mobiflight presets. I would check both places, the Bonanza manual (since Nick usually keeps variables as common as he can it seems) or the Mobiflight HubHop repository online, which is a community-sourced set of variables and presets for advanced binding shenanigans.
The other thing would be to put the sim in Dev mode (in 2024 at least) and then go to Tools --> Behavior and pretty Ctrl+G while mousing over the yoke buttons, it should bring up the code snippet and variable for the button in question.