My step dad's dog scrapes her knuckles when she walks?

This is a neurological symptom and definitely calls for a visit to the vet. If the German Shepherd is an old dog she may have lumbosacral stenosis (a.k.a. spondylosis, cauda equina syndrome, doggie sciatica). It is caused by inflammation that constricts the spinal nerves in the lower back. This results in partial to complete inability of the dog to feel what is going on in its hindquarters. Sometimes the dog will poop as it walks along, not realizing it. One of the cardinal signs for LS is that if you press your thumb and middle finger lightly into the depressions on either side of the spine, between the hips and the tail, the dog will sit.