The Amnish Guard stationed in front of the Circus Tent will mention that the Guard is looking for Fearhus for questioning. Apparently, he was the only person to escape the Circus Tent when Kalah cast his illusion spell and thus the only witness.
Fearghus can be found cowering really close to the tent, on top a wooden platform surrounded by caged animals. He can be questioned regarding the Investigate the circus tent quest, but isn't particularly helpful. Fearghus will explain that he was rehearsing his act of tiger-taming backstage and fled the tent as soon as he felt the tent changing shape around him, but he has no idea who was performing onstage at time, so he cannot any useful clues.
Once the quest is solved Gorion's Ward can speak to Fearghus again, at which point the animal trainer will show gratitude and head back to the circus. In reality, he will never make it there, instead he will be removed from the game for good.
Fearghus has a very minor role in Investigate the circus tent.