GAM:
gam report chrome events CHROMEOS_POWERWASH_INITIATED,DEVICE_BOOT_STATE_CHANGE todrive
This will print out a report for powerwashes. I also included boot state change to flag if a device entered developer mode (or back to verified mode). For enrolling/unenrolling info I think this might work--
gam report admin events CHANGE_DEVICE_STATE todrive
That will spit out a list of devices changes (disabled, deprovisioned, or activated). I think that retention time for both of these logs is 6 months.
*edit: more verbose command for simplified output:
gam config csv_output_header_filter "name,DEVICE_NAME,id.time,EVENT_REASON,NEW_BOOT_MODE,PREVIOUS_BOOT_MODE,ORG_UNIT_NAME,status.eventStatus" report chrome events CHROMEOS_POWERWASH_INITIATED,DEVICE_BOOT_STATE_CHANGE todrive
gam config csv_output_header_filter "name,DEVICE_NEW_STATE,DEVICE_PREVIOUS_STATE,DEVICE_SERIAL,actor.email,id.time,status.eventStatus" report admin events CHANGE_DEVICE_STATE todrive