If you are after a list of manager names, then that's not too difficult:
First write a SELECT query to return just the IDs of Managers:
SELECT DISTINCT Manager FROM Employee WHERE Manager IS NOT NULL
That returns:
Manager
1
2
3
Then use that to JOIN to the original table:
SELECT a.[Name] FROM Employee a
JOIN (SELECT DISTINCT Manager FROM Employee WHERE Manager IS NOT NULL) b
ON a.EmployeeID = b.Manager
That gives you a list of manager names:
Name
john
sara
philip
If you want the employee and their manager it's very similar:
SELECT a.[Name] AS [Manager name], b.Name AS [Supervised] FROM Employee a
JOIN (SELECT DISTINCT Manager, Name FROM Employee WHERE Manager IS NOT NULL) b
ON a.EmployeeID = b.Manager
Which will give you:
Manager name Supervised
John philip
John sara
sara celena
philip tomas