The query can be based on PER_MANAGER_HRCHY_DN table and fetch based on the manger_id by passing person id of the manager and manager level =1 and manager_type = 'LINE_MANAGER'.
Alternatively, since you need direct reports only, you can check PER_ASSIGNMENT_SUPERVISORS_F table as well. This table will be more performant.
select * from fusion.per_assignment_supervisors_f where manager_id in (select person_id from fusion.per_all_people_f where person_number like '&&person_number')
