SQL> declare
  2    vXML clob := '<?xml version="1.0" encoding="utf-8"?>
  3      <answ>
  4        <res xmlns="http://tempuri.org/">0</res>
  5        <code xmlns="http://tempuri.org/">111</code>
  6      </answ>';
  7    vRes number;
  8  begin
  9    select res into vRes
 10    from xmltable(XmlNamespaces('http://tempuri.org' as "X"),
 11                  '/answ'
 12                 passing XMLType(vXML)
 13                  columns
 14                  res number path '/res') t;
 15    DBMS_OUTPUT.PUT_LINE('vRes = '||vRes);
 16  end;
 17  /
vRes = 111

PL/SQL procedure successfully completed.

SQL>

declare
  vXML clob := '<?xml version="1.0" encoding="utf-8"?>
    <answ>
      <res xmlns="http://tempuri.org/">0</res>
      <code xmlns="http://tempuri.org/">111</code>
    </answ>';
  vRes number;
begin
  select res into vRes
  from xmltable('declare namespace e = "http://tempuri.org/";  (: :)
                 for $i in $d/answ/e:res
                 return $i'
               passing XMLType(vXML) as "d"
                 columns
                   res number path '.'
               ) t;
  DBMS_OUTPUT.PUT_LINE('vRes = '|| vRes);   
end;
/
vRes = 0

PL/SQL procedure successfully completed.

SQL>

declare
  vXML clob := '<?xml version="1.0" encoding="utf-8"?>
    <answ>
      <res xmlns="http://tempuri.org/">0</res>
      <code xmlns="http://tempuri.org/">111</code>
    </answ>';
  vRes number;
  vCode number;
begin
  select res,code into vRes,vCode
  from xmltable('declare namespace e = "http://tempuri.org/";  (: :)
                 let $i := $d/answ
                 return <x res="{$i/e:res}" code="{$i/e:code}"/>'
               passing XMLType(vXML) as "d"
                 columns
                   res number path '@res',
                   code number path '@code'
               ) t;
  DBMS_OUTPUT.PUT_LINE('vRes = '|| vRes);
  DBMS_OUTPUT.PUT_LINE('vCode = '|| vCode);
end;
/

vRes = 0
vCode = 111

PL/SQL procedure successfully completed.

SQL>