You should be able to see the quick in white nails. Its the pink color in the center. So you most likely be able to see where it ends in the nail and can cut up to that spot.
I believe when our dog had yeast in-between his toes we used white vinegar which we wiped on with a cotton swab. I think it cleared up pretty fast. It was really red though and stunk like corn chips.
I saw one when visiting my parents in New Jersey, only a few miles away from New York City. They are all over the place. They're masters at living in close proximity to humans, which is not a good thing for pets.