If I was doing this I would have a Department Code field (DEPTC) on the Employee Master file (EMPMAST), and then have a logical file (EMPLF01) over the Employee Master file, in Department Code (DEPTC) and Employee No (EMPNO) key order.
Your display file program would then prompt for the Department Code and read logical file EMPLF01 using the READE (Read Equal) operation code and build up your second screen (presumably a subfile) accordingly.
I wouldn’t go near OPNQRYF for this.
If you wanted to be more flexible and have screen 1 accept various parameters for record selection, e.g. Department Code, Name, Start Date Ranges, Salary Range, Marrital Status, etc, then I would use embedded SQL to provide the flexibility.
Hope this helps