I saw an episode of a program about dogs on Netflix concerning a girl with epilepsy getting a service dog.
The dog was trained to bark when she had a seizure. They didn’t mention anything about the scent, but I suspect that if she has enough seizures around the dog, he will learn to smell them before they happen. It seemed a little odd to me that he wasn’t being scent trained.
Usually they do scent training, along with other training, before they are placed with their charge. Apparently, the seizure scent is similar in all epileptics because they can train dogs with anyone’s post-seizure scent.