SQL> with 
  2    data as (
  3      select xmltype('
  4  <table>
  5    <tr>
  6      <td>A</td>
  7    </tr>
  8    <tr>
  9      <td>B</td>
 10    </tr>
 11    <tr>
 12      <td>C</td>
 13    </tr>
 14  </table>
 15  ') val 
 16      from dual
 17    )
 18  select extract(value(x), '/tr') node
 19  from data, table(xmlsequence(extract(val, '/table/tr'))) x
 20  where extractvalue(value(x),'/tr/td') = 'B'
 21  /
NODE
----------------------------------------------------------------
<tr><td>B</td></tr>

SQL> with 
  2    data as (
  3      select xmltype('
  4  <table>
  5    <tr>
  6      <td>A</td>
  7    </tr>
  8    <tr>
  9      <td>B</td>
 10    </tr>
 11    <tr>
 12      <td>C</td>
 13    </tr>
 14  </table>
 15  ') val 
 16      from dual
 17    )
 18  select extract(val, '/table/tr[position()=2]') node
 19  from data
 20  /
NODE
---------------------------------------------------------
<tr><td>B</td></tr>

WITH xmldata 
  AS( SELECT xmltype('
   <table>
     <tr>
       <td>A</td>
     </tr>
     <tr>
       <td>B1</td>
       <td>B2</td>
     </tr>
     <tr>
       <td>C</td>
       <td>D</td>
       <td>A</td>
     </tr>
   </table>
   ') val FROM dual)
   SELECT 
     POSITION,
     extractvalue(column_value,'//td') p,
     existsNode  (column_value, '//*[text()="A"]') exnod
   FROM xmldata, xmltable('//tr/td' PASSING val COLUMNS POSITION FOR ORDINALITY)
   WHERE existsNode(column_value, '//*[text()="A"]')> 0;
positon p exnode
1	A	1
6	A	1