Would you write "This is Bob, the cowboy's, horse," or "This is Bob's, the cowboy, horse."?
Neither. It would be, "This is Bob, the cowboy's horse." You don't need a comma between cowboy and horse.
The first one.
Personally i would probably write, The horse is Bob, he is the cowboy's. Or the cowboy's horse was named Bob.
the first one
Try to say that five times fast !