You can get that information from icx_sessions table
select f.user_name ,to_char(i.creation_date,'DD-MON-YY HH:MI:SS'),
from icx_sessions i, fnd_user f
where i.user_id = f.user_id
and i.creation_date between sysdate-30 and sysdate;
You can change the where clause or remove columns.
This query will show you same user multiple times because this table captures each login and change of responsiiblity.
So you can filter as per your requirement.
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Thanks a lot for this avigation.