If you have the rowid, then you can use the DBMS_ROWID package to obtain the object name for the table that holds this row. To obtain the object_id of the table, use the following query:
SELECT DBMS_ROWID.ROWID_OBJECT('rowid') FROM dual;
Make sure you insert your rowid into the function above. Once you know the object_id, you can query V$LOCKED_OBJECT similar to the following:
SELECT session_id,oracle_username,locked_mode FROM v$locked_object WHERE object_id = xx;
Obviously, you will replace 'xx' with the object id returned from your call to DBMS_ROWID.