You should make a search on the forum (mod section). There’s a very detailed and well done guide on pet builds in Grim’ with like dozens of build propositions and great explanations. Edit: which has been already linked while writing my answer
I don’t play Grim anymore but my favorite builds were:
Medea already linked up my thread, but since you asked for Terror Knight specifically, I have 2 builds with that class, and depends on what type of pets you’d like to build with:
Pet-Scaled Pets: This follows the traditional Summoner Blueprint, meaning you will build around your pets’ damage (with the extra benefit of these pets being functionally immortal).
Blood Knight Set: This build has multiple pets; the difference between these pets and the other pets is that these pets are built around player damage, so you build around getting lots of damage bonuses for yourself, and your pets are similarly strong as well.