Bald Spot

Possibly ringworm. Any other info, is it red, itchy?

No it is not red, and doesn't seem to bother him.
Miller

Hair loss on dogs may be caused by a number of problems. Generally it is caused from the dog having an allergic reaction to something associated with or in the environment of the dog. Tests can be carried out by your vet to determine what the dog is allergic to, but generally are due to either pollens in the air (generally in spring), dietary habits or flea bites. It is interesting to note that one flea bite can still be causing an effect on a dog up to seven days later. We call this single spot of hair loss "focal alopecia" It is more common in small breeds, but not unheard of in larger breeds, and is sometimes caused by to much progesterone or testosterone. Your vet can help you work this out.