How to find the AD user that logged in to SQL Server using SQL Login Some users are logging into database servers locally, opening SSMS and logging in to SQL Server using SQL logins to run queries.

How can I find the AD user that logged in to SQL Server using a SQL login on the local database server using SSMS?
It's not possible I'm afraid.  This is one of the down sides of using SQL Server logins.  The only thing you can do is to look at the Hostname.  Most people connect using their local machine and if your company has a list of user to machine name then you can track them that way.

Unfortunately this information is not normally logged.  You will have to set up a trace, extended events session or server audit and collect login events and make sure you include the hostname property.