My puppy ate a toy eye and is drooling. When should I call the vet?

I'm sorry to hear Jax ate something he shouldn't! This is unfortunately a common behavior in puppies so hopefully he grows out of it.
With an object as small as that little plastic eye, it should likely pass through with minimal issue for Jax. If he ate it very recently (within the last hour or two) you could go to your vet where they can use special medication to make him vomit, and hopefully bring the piece of plastic back up. If it's been longer than that then I recommend monitoring Jax carefully, ensure that he continues eating and drinking normally, and check his stool each time he poops to see if the piece of plastic has passed. If you notice that Jax becomes lethargic, goes off his food, or starts vomiting then you need to schedule a visit with your regular veterinarian for a thorough physical exam and possibly some X-rays to check for an obstruction.
Since Jax has now shown us that he likes to chew on things it would be recommended to only offer toys that are safe for him to chew, with no extra pieces that might come off. And if he starts to shred a toy then it is time to replace it as even pieces of fabric can cause obstruction issues.