Do not use the $dbobject_dml_getData() method , use $dbobject->getData() instead.
When you construct the WHERE string you must remember to enclose non-numeric values with single quotes.
The result returned by getData() is a 2-dimensional array which is keyed by row numnber, with the value being an associative array of name=value pairs. Your code should therefore look like this:
$dbobject =& RDCsingleton::getInstance('htm_db_kontakte');
$where = "kontakt_name='{$select_array['user_id']}' AND kontakt_vorname='{$select_array['user_seq_no']}'";
$data = $dbobject->getData ($where);
if (!empty($data) {
$data = $data[0];
$fieldarray['kontakt_ma_name'] = $data['kontakt_name'];
$fieldarray['kontakt_ma_vorname'] = $data['kontakt_vorname'];
} // if