ORA-00907 Missing right parenthesis issue - select with order by inside insert query

Both the current answers ignore the fact that using order by and rownum in the same query is inherently dangerous. There is absolutely no guarantee that you will get the data you want. If you want the first row from an ordered query you must use a sub-query:

insert into my_tbl ( col1, col2 )
select data, 'more data'
  from ( select data
           from fir_tabl
          where id = 1
          order by created_on desc )
 where rownum = 1
       ;

You can also use a function like rank to order the data in the method you want, though if you had two created_on dates that were identical you would end up with 2 values with rnk = 1.

insert into my_tbl ( col1, col2 )
select data, 'more data'
  from ( select data
              , rank() over ( order by created_on desc ) as rnk
           from fir_tabl
          where id = 1)
 where rnk = 1
       ;