declare
  type acc_inf is record(
    code varchar2(25),
    name varchar2(4000));
  type acc_inf_arr is table of acc_inf;

  type all_inf is record(
    num_doc number,
    acc_all acc_inf_arr);
begin
  -- нужно создать ксемельник по all_inf
  -- где во вложенном массиве acc_all может быть несколько записей

  null;
end

SQL> select xmltype(cursor(select 666 num_doc,
  2                               cursor(select rownum code, 'name' || rownum name
  3                                        from dual
  4                                      connect by rownum <= 3)
  5                                  acc_all
  6                          from dual))
  7            x
  8    from dual;

X
----------------------------------------------------------------------------------------------------
<?xml version="1.0"?>
<ROWSET>
 <ROW>
  <NUM_DOC>666</NUM_DOC>
  <ACC_ALL>
   <ACC_ALL_ROW>
    <CODE>1</CODE>
    <NAME>name1</NAME>
   </ACC_ALL_ROW>
   <ACC_ALL_ROW>
    <CODE>2</CODE>
    <NAME>name2</NAME>
   </ACC_ALL_ROW>
   <ACC_ALL_ROW>
    <CODE>3</CODE>
    <NAME>name3</NAME>
   </ACC_ALL_ROW>
  </ACC_ALL>
 </ROW>
</ROWSET>

SELECT  (XMLElement("TAG",
        xmltype('<kkk> fkjvnhfjkvnh </kkk>'),
        XMLAgg(XMLElement("ResultTag",
            XMLElement("sacc_number", acc.code),
            XMLElement("sacc_name",null))))
    ).GetStringVal() as TAG
  FROM eid.eid_firma_account acc
 where reference in (1199547, 98822715)
 and branch = 191
 
 
 SELECT  (XMLElement("TAG",
        xmltype('<kkk> fkjvnhfjkvnh </kkk>'),
        XMLElement("ResultTag",
            XMLElement("sacc_number", acc.code),
            XMLElement("sacc_name",null)))
    ).GetStringVal() as TAG
  FROM eid.eid_firma_account acc
 where reference in (1199547, 98822715)
 and branch = 191