Array
(
    [uuid] => 32eeda5f-270f-477d-b24c-75ed15e69b2a
    [langcode] => en
    [status] => 1
    [dependencies] => Array
        (
            [module] => Array
                (
                    [0] => node
                    [1] => taxonomy
                )

        )

    [id] => node.field_event_type
    [field_name] => field_event_type
    [entity_type] => node
    [type] => entity_reference
    [settings] => Array
        (
            [target_type] => taxonomy_term
        )

    [module] => core
    [locked] =>
    [cardinality] => 1
    [translatable] => 1
    [indexes] => Array
        (
        )

    [persist_with_no_fields] =>
    [custom_storage] =>
)

Drupal::config('field.storage.node.field_event_type')->get();

$handler = $field_data['settings']['handler'];

$bundle = 'page';
$vocs = [];
$flds = Drupal::service('entity_field.manager')
  ->getFieldDefinitions('node', $bundle);
foreach ($flds as $fld) {
  $hand = $fld->getSettings()['handler'];
  if ($hand == "default:taxonomy_term") {
    $fldnm = $fld->getName();
    $config = $fld->get('dependencies')['config'];
    foreach($config as $cf){
      if(strpos($cf,"taxonomy.vocabulary") !== FALSE){
        $vocs[$fldnm] = str_replace("taxonomy.vocabulary.","",$cf);
      }
    }
  }
}
dpm($vocs);