To protect your sock, the knife should be in a sheath of some sort, which is then tucked into the top of the sock on your dominant side. If you're right-handed, use the right sock. If left-handed, use the left. It should stick out of the top of the sock enough to be easily gripable when the need for it arises, and, since many sgianan dubh have decorated grips and/or stones in the pommel, it should show enough to be seen.

Good enough?

Robert beat me on the draw.