I got a redemption ticket for my partner with SIA on class D (outward) and I (return) on IST-SIN-IST.

I got a redemption ticket for my partner with SIA on class D (outward) and I (return) on IST-SIN-IST. Obviously it is not possible to claim miles on Krisflyer (Gold). However as he is also Gold with Turkish Airlines, could the miles be credited to the Miles and Smiles account?

AFAIK you can attach only one program to ticket and since ticket been redemption one SQ program is attached.

That is incorrect.

If you had purchased a revenue tickets with SQ and appended your Krisfkyer number but subsequently (prior to flying) chose to accrue to   Turkish's programme, you would be able to do so and earn miles with the Turkish programme.

However, given that this was a redemption booking, you will not earn any miles regardless of which FF number you append to the booking. So while you may choose to append the Turkish FF number to reflect Star Gold status for baggage, priority access and lounge purposes, those flights will not accrue mileage. 

Those flights will not accrue mileage. I class is the general "saver" redemption booking code that all of star alliance uses. It will not earn any miles on any star alliance frequent flyer program. 

D class is an additional code that SQ  uses for "standard" redemption bookings, which cost a bit more in Krisflyer miles. It is however, ALSO, rather inconveniently, a revenue booking code - Both these "D's" are NOT the same however. The difference is that the one paid with miles is inhibited from accruing miles through a computer entry made in a particular field on your booking (i forget which, but was shown to me some time back). This inhibitor will also cause (rightly) no miles to be accrued.