$sql ="Select * FROM event_mgmt_registration r WHERE event_nid = $node->nid AND reg_id = $reg_id";

$node = node_load($nid);
$reg_trans_raw = db_select('event_mgmt_registration', 'r')
 ->fields('r')
 ->condition('event_nid', $node->nid, '=')
 ->condition('reg_id', $reg_id, '=')
 ->execute();
$reg_trans = $reg_trans_raw->fetchAssoc();

drupal_set_message(print_r( 'Fetch Assoc: '.$reg_trans , true));

->condition('event_nid', $node->nid, '=')