what's wrong with my code?

Again you have not given clear details like to table structure for frieight field.

Still check below query as we dont have table structure of anyone,

SELECT TOP 1 e.EmployeeID, (reqTotalOrderPrice + ORD.Freight) as TotalAmount, TotalOrders
FROM ( SELECT e.EmployeeID, (SUM(TotalOrderPrice)*0.1) AS reqTotalOrderPrice, COUNT(o.OrderID) as TotalOrders
 FROM Employees e
 INNER JOIN Orders o
 ON o.EMployeeID = e.EmployeeID
 INNER JOIN (SELECT OrderID,SUM((UnitPrice * Quantity) - Discount) AS TotalOrderPrice
 FROM [Order Details]
 GROUP BY OrderID
 )oi
 ON oi.OrderID = o.OrderID
 GROUP BY e.employeeid 
 ) RSET
 INNER JOIN Orders ORD ON RSET.EmployeeID = ORD.EmployeeID 
ORDER BY reqTotalOrderPrice DESC,TotalOrders ASC