CREATE TABLE Test (
  ID              INTEGER,
  Date_operation  DATETIME,
  Identifikator   INTEGER
)
GO

INSERT INTO Test VALUES (2, '2015-05-28T00:00:00', 1)
INSERT INTO Test VALUES (3, '2015-06-15T00:00:00', 1)
INSERT INTO Test VALUES (5, '2016-07-24T00:00:00', 2)
INSERT INTO Test VALUES (6, '2016-08-24T00:00:00', 2)
GO

WITH T (ID, OperationDate, PartitionID, RowNumber)
AS
(
 SELECT *, ROW_NUMBER() OVER(PARTITION BY Identifikator ORDER BY Date_operation DESC)
 FROM Test
)
SELECT PartitionID, OperationDate FROM T WHERE RowNumber = 1
GO

DROP TABLE Test
GO