SELECT dbms_xmlgen.getxml
('SELECT USER_DATA 
FROM <Queue_table> X 
WHERE X.USER_DATA.SALE_ORDER.P_HEADER_REC.ORIG_SYS_DOCUMENT_REF=800501298') 
FROM dual;

--create needed SQL TYPE
CREATE OR REPLACE TYPE my_tab_row_type AS OBJECT (
  tabnam   VARCHAR2 (30),
  nrows    NUMBER
);
/

--test TYPE
SELECT my_tab_row_type (table_name, num_rows) xstr
  FROM user_tables
 WHERE ROWNUM <= 3;

--select as XML, use DBMS_XMLGEN.getxmltype !
WITH xml_data AS
 (SELECT DBMS_XMLGEN.getxmltype
   ('SELECT table_name, num_rows, blocks FROM user_tables WHERE rownum<=3') xstr FROM DUAL)
SELECT *
  FROM xml_data;

--select as TYPE via XML
WITH xml_data AS
 (SELECT DBMS_XMLGEN.getxmltype
   ('SELECT table_name, num_rows, blocks FROM user_tables WHERE rownum<=3') xstr FROM DUAL)
SELECT my_tab_row_type 
        (EXTRACTVALUE (COLUMN_VALUE, '//TABLE_NAME'),EXTRACTVALUE (COLUMN_VALUE, '//NUM_ROWS')) mtrt
  FROM xml_data, TABLE (XMLSEQUENCE (EXTRACT (xstr, '//ROW'))) 

MTRT                                              
--------------------------------------------------
(TAB_A; 2)                        
(TAB_B; 19)                      
(TAB_C; 171)                      

3 rows selected.