How do I discover property names?
You can use the EntityFieldManager. This is an example how to get the properties for the field uid of the entity node:

$fields = \Drupal::service('entity_field.manager')-&gt;getFieldStorageDefinitions('node');
$properties = $fields['uid']-&gt;getPropertyDefinitions();


From the command line you can use this in a drush php-eval command:

drush ev "var_dump(\Drupal::service('entity_field.manager')-&gt;getFieldStorageDefinitions('node')['uid']-&gt;getPropertyDefinitions())"