In Torchlight there are wearable rings that boost experience gain by a percentage. If I equip my pet with one of these rings, will this increase the experience gain of my player?
It is unlikely that your pet's +%xp affects your own.
Looking at the similar stat of +% magic find, I know that if you give your pet +Magic Find items, they will benefit from the magic find only when they kill things (as opposed to you killing them. Your pet has magic find = to your magic find + any magic find items worn by the pet.
But the way this concept would work for XP is, if you have a +3% xp ring, and your pet has a +2% xp ring, you would get 103% XP, and your pet would get 105% (all of your xp%, + it's own). However, since pets don't accrue experience, this is irrelevant.
There was a change in Patch 1.2 that sheds some light on this:
If your pet's trinkets give a total 2% magic find boost, and your own equipment has a total 3% magic find boost, then you will only receive a 3% find rate boost.
I think the meaning of the change is that pre-patch pets and minions would have had their own drop rate that applied whenever they made a kill. The change simplifies the situation, so you don't need to have drop rate boosts for yourself and your pet.
However, it isn't clear if this applies to experience as well.