If you have dept name in the emp file as you have posted, you read a record, move the data to a print line, write the report file from the print line, and continue until end of file.
If, as is more likely, you have dept id in the emp file, then you first read all dept file records into a table in WORKING-STORAGE. You then read each record of the emp file, search the table for the dept id (which you can do yourself or use the SEARCH verb in COBOL) and use the associated dept name in the print line.
Note that we will help you on this forum, but this is NOT a write-the-code-for-you forum. If you want code written for you, be prepared to pay the daily rate for whoever agrees to write the code (and daily rates are typically 500 to 1000 U.S. dollars per day).