SQL> with 
  2    data as (
  3      select 
  4  xmltype('<A>
  5  <b>
  6  <c>
  7  <col>val1</col>
  8  <col>val2</col>
  9  <col>val3</col>
 10  </c>
 11  <c>
 12  <col>val7</col>
 13  <col>val8</col>
 14  </c>
 15  </b>
 16  <b>
 17  <c>
 18  <col>val10</col>
 19  </c>
 20  <c>
 21  <col>val11</col>
 22  <col>val12</col>
 23  </c>
 24  </b>
 25  </A>') x
 26      from dual ),
 27    b as (
 28      select column_value b, rownum rn
 29      from data, table(xmlsequence(extract(x,'/A/b')))
 30    ),
 31    c as (
 32      select column_value c, rownum rn
 33      from (select b from b where rn=2), table(xmlsequence(extract(b,'/b/c'))) 
 34    )
 35  select extractvalue(value(c),'/col') val
 36  from (select c from c where rn=1), table(xmlsequence(extract(c, '/c/col'))) c
 37  /
VAL
------------
val10

1 row selected.