Using your knee almost like a Scott Curl pad, and bringing the dumbbell to the opposing shoulder, predominantly hits the Biceps Brachii (Biceps head). Bringing the dumbbell to the same shoulder (Dumbbell Concentration Curls - Same Shoulder) hits both the Biceps Brachii and Brachilias.
Although Dumbbell Concentration Curls to the Opposite Shoulder is a popular gym exercise, it's far down my list of biceps exercises and it's not often I ask a client to perform this exercise.
For more biceps exercises, visit our Exercise Index.
For ideas of how best to incorporate this exercise into your training regime, please consider the purchase of the acclaimed Gym Workouts: Maps to Success or download (for free!) our workout app GP Shuffle.