Have not tested this, but :

SELECT COUNT(DISTINCT datakey) OVER(Partition by datakey) AS Uniquedatakey,

COUNT(DISTINCT CASE WHEN landline<>'' THEN landline END) OVER(Partition by datakey) AS Uniquelandline,

COUNT(DISTINCT CASE WHEN mobile<>'' THEN mobile END) OVER(Partition by datakey) AS Uniquemobile,

COUNT(DISTINCT CASE WHEN email<>'' THEN email END)OVER(Partition by datakey) AS Uniqueemail

FROM test