How much damage do I have to inflict onto an enemy to still get XP even if a companion/someone other than me finishes them off?

Solution 1:

This mod changes the amount of damage you need to do to an enemy in order to receive xp for that enemy when it dies. By default you need to do 25% of the total damage done to the enemy in order to gain xp.

Lower Damage Requirement For XP (Fixed Companion Kills)