Eric Porthe is a Basic Dispelling Trainer and can teach Dispel levels from 0-3.
Eric can be found Adessa - The Walls usually walking around in front of Adessa Prison, not far from the player's home Sandstone Villa(Quest:Hand-Delivered must be completed), or in the Arcadium building. Eric can also be found in Adessa - The Isles in the Forum.
More than one user has reported that, in their game, Eric Porthe was labeled as a persuasion trainer on the map even though he still acted as a dispelling trainer. However, this is because he is usually out and about and not always in the Forum. The Forum is also the usual location of the persuasion trainer Templar Montainel. It is likely the labels for what's in the location are hard coded and therefore don't update if he has entered the Forum.