[Uh... the background noise for this specific audio feed is horrendous. It sounds like Gorthan is in a large, crowded room where several people are yelling or talking loudly.]

It is actually quite easy. Most of them are rather expressive creatures, even those who lack facial features and means of expressing emotions that we consider conventional. Do not be afraid to spend time with them as much as you can, and you will learn to pick up on the signs quickly enough.

Also, as I am sure you have realized, gaining experience in battle contributes to their satisfaction with themselves, and, by reflex, with their trainer.