In most cases this Slam is a done deal.
On a ♣ or a ♥ opening lead Declarer gets a free finesse against the ♣Q or the ♥J and the contract is in the bag.
But even on a diamond lead the contract should usually not be difficult to make.
Remove Opponents' trumps, discard two of Declarer's diamonds on Dummy's ♠K and ♠Q, and if the ♣ finesse is successful Declarer wins all 13 tricks.
However in this case there is a sting in the tail.