If it's sysadmin level, likely it doesn't own any objects as it would have mapped in as dbo to each database. What you can do:

- query sys.database_principals in each DB to see if there are any users that have a matching SID to the login (sys.server_principals).

- If that shows up as positive, query sys.objects, sys.schemas, etc., to see if there are any owned objects, etc.

- Again, if that shows up as positive, query sys.database_permissions in each DB to see if there are explicit permissions for that user (also check roles and permissions assigned to those roles)

- Do the same thing against sys.server_permissions as you did against sys.database_permissions

Again, this only tells you anything explicitly assigned. If it had access as a member of the sysadmin role, chances are there are no explicit objects owned and no explicit permissions. In this case, your best bet is to use a server side trace filtered to capture the actions of just that login.