This question is somewhat related to my earlier question How are the compositional components of exoplanet atmospheres differentiated?, but this about a specific surface-atmospheric phenomena - volcanism.
Using our solar system as a rough analogue (where asides from Earth, Venus, Io and Triton have active volcanism, probably more), volcanism should be not uncommon amongst exoplanets given the right conditions. Obviously, we could probably only detect either the massive shield, plateau volcanism, or prolonged volcanism from multiple vents.
What observational constraints are there in detecting the presence of volcanism on exoplanets?