If you want to find, when a table was last modified like insert,update ,delete, then use the dictionary table dba_tab_modifications.

SCENARIO:

1. Insert into test data:

2. Check dba_tab_modification:

 

As you can see, the dba_tab_modification is not showing any rows. Now you need to flush the info , to update the dba_tab_modification table.

3.Flush the monitoring Info

 

Now you should be the able to see the last modified information from dba_tab_modification. If you want to see, when a DDL change happened to the table , then use the below query.