Check all enabled trace events Recently  on a database I enabled trace for event 12842 using the below statement in order to trace Oracle error ORA-12842 : Invalidated cursor.

alter system set events '12848 trace name ERRORSTACK level 3';


After sometime the error did occur but we could not find any trace file for that event.

I am suspecting the tracing got disabled after instance restart.

Is there any way to list out all the events for which tracing is enabled ?
I got my answer from the below link: 
generate/analyze trace for error 1461

One may know by using the following statements in sqlplus: 

oradebug setmypid 
oradebug eventdump system


This did the magic :)