Using “oradebug dump events 1” one can find/list events set in a session.
For example:
In a session events 10046 and 1410 events are set
SQL> ALTER SESSION SET EVENTS='10046 trace name context forever, level 12';
Session altered.
SQL> ALTER SESSION SET EVENTS='1410 trace name context forever, level 12';
Session altered.
SQL> SELECT distinct sid FROM v$mystat
SID
———-
131
In another session login as an account as sysdba
SQL> SELECT pid, spid FROM v$process where addr IN (SELECT paddr FROM V$session where sid = 131);
PID SPID
———- ——-
12 3420
SQL> oradebug setorapid 12
Unix process pid: 10932, image: oracle@localhost.localdomain (TNS V1-V3)
SQL> oradebug dump events 1
Statement processed.
SQL> oradebug tracefile_name
/u01/oradata/admin/TEST/udump/test_ora_10932.trc
Or in 11g:
SQL> oradebug eventdump session
1410 trace name context forever, level 12
sql_trace level=12
After running the above oradebug will dump the events in the trace file in the above case /u01/oradata/admin/TEST/udump/test_ora_10932.trc shows event 1410 and 10046 events set.
…
Dump event group for level SESSION
TC Addr Evt#(b10) Action TR Addr Arm Life
974FED50 1410 1 974fede0 0 0
TR Name TR level TR address TR arm TR life TR type
CONTEXT 12 0 -1 2 0
974FEBF8 10046 1 974fec88 0 0
TR Name TR level TR address TR arm TR life TR type
CONTEXT 12 0 -1 2 0
*** 2010-07-15 23:40:05.671
..
alexlima.com 
this is easier method from Julian Dyke
Listing Enabled Events
To check which events are enabled in the current session
SET SERVEROUTPUT ON
DECLARE
l_level NUMBER;
BEGIN
FOR l_event IN 10000..10999
LOOP
dbms_system.read_ev (l_event,l_level);
IF l_level > 0 THEN
dbms_output.put_line (‘Event ‘||TO_CHAR (l_event)||
‘ is set at level ‘||TO_CHAR (l_level));
END IF;
END LOOP;
END;
/
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