Top wait events indicate what is the major performance problem in your database system. To get the top wait event, click "Top Event" butten or press F7. A top event window will be shown as below.
In this window, you can find the load (percent) caused by each wait event. And you can get as many top events as you want, or you can check the history top event by changing the time slot.
And you want to see the top waiting object, then change the top type as "Wait Objects". The content of the table will be changed as below.
Alternatively, if you want to see the top wait event as well as the top waiting object of each event, you can change it to "Event and Object"