Hola! prueba con esto que a mi me funciona... Saludos.
select column_name from ( select rownum nro_fila, a.* from user_tab_cols a where a.table_name = '&NOM_TABLA' ) where nro_fila = (SELECT ROUND(DBMS_RANDOM.value(0,(select COUNT(*) from user_tab_cols a where a.table_name = '&NOM_TABLA' ) ) ) FROM DUAL )