How to show fields in the Inline Entity Form display widget?
Use hook_inline_entity_form_table_fields_alter() this is what I am using on a current site: 

function MY_MODULE_inline_entity_form_table_fields_alter(&amp;$fields, $context) {
  //Determine the bundle and entity type from $context

  unset($fields['id']); //&lt;get rid of the id field

  //add any fields you need to the $fields array
  $fields['FIELD_NAME'] = array(
    'type' =&gt; 'field',
    'label' =&gt; t('FIELD'),
    'weight' =&gt; 2
  );

}