Your XML seems to be missing a root node? If your XML data is as you show it, you can get XMLTable() function to parse it if you put it in a dummy root node, for example like this:
select x.firstname
from mytable,
xmltable(
'/rootnode'
passing xmltype('<rootnode>'||myclobcol||'</rootnode>')
columns
firstname varchar2(100) path 'firstname'
) x
If you need to get multiple values at the same time, you just add to the columns clause:
select x.*
from mytable,
xmltable(
'/rootnode'
passing xmltype('<rootnode>'||myclobcol||'</rootnode>')
columns
firstname varchar2(100) path 'firstname',
lastname varchar2(100) path 'lastname',
middleini varchar2(10) path 'middleinitial'
) x