I'm making a mod that enhances necromancy. Now I want to create a Perk that makes pets absorb health when hitting enemies and transfer a certain amount to the necromancer. I'm kinda lost on this one and any help would be much appreciated.

Depending on how you wish to approach this, i have a similar system in place except i dont use a perk

I have a spell which conjures multiple rodents depending on level. Each rodent has a chance of applying a drain health spell.

The drain health spell is applied through the attack data of the summoned creature (actor).

As for transfering health back to the caster, i use a script on the magic effect to cast a second drain effect from the player to the summoned pet. The second drain effect from player to pet is non-hostile (unflag hostile) and the pet won't attack you.
This then gives the illusion of health transferring from the target to the pet and then onto the player

This is a script that i made which has the above effect