It's very hard to answer a question based on such limited information. My answer thus may not work for you due to that lack of information.
In FileMaker, you can set up a field to auto-enter serial numbers. Each time you create a new record, a new unique value is entered into this field and it's the next number in the specified series. So if you have a table of exams with one record for each exam, an Exam Number field can be set up in this table using field options that auto-enters a serial number for you.