This piece of code show the list of events, set in the Oracle database
set serveroutput on
declare
event_level number;
begin
dbms_output.enable(20000) ;
for i in 10000..33999 loop
sys.dbms_system.read_ev(i,event_level);
if (event_level > 0) then
dbms_output.put_line('Event '||to_char(i)||' set at level '||
to_char(event_level));
end if;
end loop;
end;