I saw a lil Pom howling on a YouTube video once. The dog was watching a YouTube video of howling wolves. Track that video down and you could have a video of your Pom watching a Pom watching a video of wolves. Or you could just play a video or sound clip of wolves howling and bypass all the rest of it. Sometimes works for my dogs.
Dogs will howl (in their own doggy voice..they are not wolves by a long shot) if you subject them to certain high pitched sounds. They are not singing/howling for you or because they like the sound. It actually hurts their ears...they are trying to respond to pain. So don't try to make your ball of fluff howl that way, please. Maybe you should try a basset or hound dog if you want to hear howling.