User below query to get the top wait classes in Oracle database

Select wait_class, sum(time_waited), sum(time_waited)/sum(total_waits)
From v$system_wait_class
Group by wait_class
Order by 3 desc;

From the above query, supply each wait class into below query to get the top wait events in database with respect to particular wait class

Select a.event, a.total_waits, a.time_waited, a.average_wait
From v$system_event a, v$event_name b, v$system_wait_class c
Where a.event_id=b.event_id
And b.wait_class#=c.wait_class#
And c.wait_class = '&Enter_Wait_Class'
order by average_wait desc;