stock_date       sku
----------       ---
2016-06-01         0
2016-06-02       123
2016-06-03       123
2016-06-04       123
2016-06-06       123
2016-06-07       123
2016-06-03       245
<... &c...>

sku     1   2   3   4   5   6   7
---     -   -   -   -   -   -   -
123     0   Y   Y   Y   0   Y   Y
245     0   0   Y.... &c.

SELECT
    sku,
    MAX (CASE WHEN stock_date = '2016-06-01' THEN 'Y' ELSE 'N' END) AS [1],
    MAX (CASE WHEN stock_date = '2016-06-02' THEN 'Y' ELSE 'N' END) AS [2],
    MAX (CASE WHEN stock_date = '2016-06-03' THEN 'Y' ELSE 'N' END) AS [3],
    ...
FROM
    dbo.mytable
GROUP BY sku