Things that DO help pet thorns
Thorns
Primary Stat
Physical Damage % on gear
Buffs to the creature (ie %skeleton damage)
Njar’s Black Death, but only if the pet rune selected is poison-type
Bonuses from legendary affixes
%damage vs elites
Enforcer gem
Things that do NOT help pet thorns
Crit hit
Crit damage
Attack Speed
Base weapon damage
Ring/amulet +damage
%damage on weapon
Poison % on gear (even when using poison-type pets)
Tasker and Theo
I tested all of these earlier today. A bit surprised that attack speed and tasker/theo didn’t change the thorns damage at all since many forums suggest otherwise. I do not think area damage can proc from thorns but was hard to test.
I also found something strange with the thorns changes when adding int. Each point of int increased the thorns damage, but with diminishing returns. 1% to 0.4% extra damage per point when adding 100-1500 int.