In the above link are three pictures of my dogs nails. I've visited several sites regarding trimming black nails but I'm still unsure. He was last at the groomers exactly 2 weeks ago when I took those pictures.
I hear clicking noises when he walks and this was straight from the groomers even though we're supposedly not supposed to hear it. This is one of the reasons why I'm afraid to clip any more nail. The other reason is that the circles as shown in the pictures have got me paranoid about the proximity of the quick. The third reason is I don't know if they've been let to grown.
Sorry I can't provide any more information as I'm not the original owner of the dog. I've had him for exactly 2 weeks and he's 2.5 years old and this is my first pet ever.