Investigating an Oracle 12c outage after the fact, while limited to SQL*Plus
You can inspect V$SQL for statements that don't use binds, eg.

select substr(sql_text,1,80), count(*)
   from v$sql 
   group by substr(sql_text,1,80)
   order by count(*) desc


Then inspect the full text of the statements that come on top, see where they differ.