Does this return what you expect?
Select (e.FirstName + ' ' + e.LastName) as EmployeeName,
c.CustomerID,
o.OrderID,
o.OrderDate,
SUM((r.UnitPrice * r.Quantity) - (r.UnitPrice * r.Quantity * r.Discount)) as OrderAmount
FROM Orders o
Inner Join Employees e
On e.EmployeeID = o.EmployeeID
Inner Join Customers c
On c.CustomerID = o.CustomerID
Inner Join [Order Details] r
On r.OrderID = o.OrderID
Group by e.FirstName,e.LastName,c.CustomerID,o.OrderID,o.OrderDate,e.EmployeeID
Order by EmployeeName,c.CustomerID,o.OrderDate,o.OrderID