I'm confused as to what you're trying to teach. Trotting is a gait that any dog will do if you go the right speed. It's roughly defined as when their opposite legs come together, as opposed to pacing when the legs on the same side move out and back together (slower), or running.
See this short youtube video on different gaits.
If you're asking about the dog having that high stepping trot during heeling, it is accomplished by getting the dog to put his weight on his rear so the front legs are free for that reach. Teaching the dog to heel with his head very high naturally results in this movement. Also having the dog pop up to get his reward in heel position (instead of bringing the treat to him) encourages that weight to be on the rear.
Does that help?