Smell

Is there a prohibition against smelling treif, such as roast pork?

Something which is prohibited to eat, but has no prohibition of other benefit (e.g wearing it as a garment) such as pork, is permitted to smell if it's main purpose is not for fragrance. If it is a fragrant spice, there is a dispute as to whether one may smell it. If it is something from which all benefit is prohibited, like meat cooked in milk, smelling is also prohibited.