How to enumerate all possible `adb shell input keyevent` codes for a device?

I have a damaged screen and touch digitizer on an automotive head unit. I am trying to access the diagnostics menu for the unit (Honda Clarity 2018 PHEV non-touring), but the touch input keys are not (to my knowledge) among the standard Android keyevent codes. Is there some way to pull these directly from the head unit itself? I have root on the unit, and I did find some keyboard data files but the enclosed keyevent codes don't appear to all be functional, and it isn't clear from the descriptors which keys would match with the necessary inputs (Power, Menu, and Screen Brightness, the first two of which are not the standard Android ones). EDIT: here's a picture of the keys in question. Note that these do **not** correspond to the Android generic equivalents, e.g., keyevent 24 & 25 will invoke the Android native UI's volume control, but not the same as these keys; same for the rest of the keys.