I think there's perhaps a problem with either your input data, or example output, since your last output row doesn't seem to match any of your inputs.
I think you're asking for a dynamic pivot, something like this:
Test data
SET DATEFORMAT DMY
CREATE TABLE #Test (CustId INT, Date DATE, ArtikelNr INT)
INSERT INTO #Test VALUES
(1,'23.02.2016',50),
(1,'14.02.2016',40),
(2,'22.02.2016',40),
(1,'24.02.2016',50)
Query
DECLARE @Query AS NVARCHAR(MAX)
DECLARE @Cols AS NVARCHAR(MAX)
SELECT @Cols= ISNULL(@Cols + ',','') + QUOTENAME(RN) FROM (SELECT DISTINCT ROW_NUMBER() OVER (PARTITION BY CustId, ArtikelNr ORDER BY CustId) RN FROM #Test) Z
SET @Query =
N'SELECT * FROM
(SELECT *, ROW_NUMBER() OVER (PARTITION BY CustId, ArtikelNr ORDER BY CustId) RN FROM #Test) A
PIVOT ( MIN(DATE) FOR RN IN ('+@Cols+')) PVT
ORDER BY CustId, ArtikelNr DESC'
EXEC sp_executesql @Query
CustId ArtikelNr 1 2
----------- ----------- ---------- ----------
1 50 2016-02-23 2016-02-24
1 40 2016-02-14 NULL
2 40 2016-02-22 NULL