We are looking for SQL query which can pull the list of employee whose assignment data is missing

Basically,I am trying to set up a query that will find records that are missing data. For example, I have a main form where users will enter biographical data, but they may be missing the birthday, the last name, and the phone number or in assignment page user has missed the Grade, location to enter. The idea is that this query will help us identify the records which are missing data and allow us to then go back and enter this data in when we find it. How would I set up the query to catch the