No, that is not possible.
"For each row returned by a query, the
ROWNUMpseudocolumn returns a number indicating the order in which Oracle selects the row from a table or set of joined rows. The first row selected has a
ROWNUMof 1, the second has 2, and so on."
So it means that rownum is not a part of data but just a number of record in resultset (it could be treated as unique).
To find duplicates you have to have a condition of duplicate (f.e. a name meets twice).
from (select *,
row_number() over (partition by emp_name ORDER BY employee_id) rn
S Paul RJ