Figured it out - apologies for posting dumb questions. For the record
gam print users allfields custom all
Will get all the custom fields. For GCPW, the fields are
customSchemas.Enhanced_desktop_security.AD_accounts.0.value
customSchemas.Enhanced_desktop_security.Local_Windows_accounts.0.type
customSchemas.Enhanced_desktop_security.Local_Windows_accounts.0.value
Hopefully that saves someone a step