WITH CTE AS
(
    SELECT  *,
            RN = ROW_NUMBER() OVER(PARTITION BY Id_Empleado ORDER BY Dias DESC)
    FROM dbo.Contrato
)
SELECT  E.Nombre,
        E.Identificacion,
        C.Dias
FROM dbo.Empleado E
INNER JOIN CTE C
    ON E.Id_Empleado = C.Id_Empleado
WHERE C.RN = 1;