Shattered Kingdoms

If you have a pet in the front row and it kills the target do you still gain exp? a percentage? or what?

You don't gain exp from your pets. You don't gain exp based on NPC kills, though, but rather based on the percent of damage you do to them as they are dying. So if your pet kills your target while you're EXPing, you're not having your own pets killsteal.

You don't 'get experience from the kill.' You get experience for all the damage your actual character does, so you don't need to land a kill blow to 'get all the exp. from that NPC. I realize that was part of the question you were asking also.
If your pet is the only thing damaging the NPC, you'll get nothing, so be sure to be whacking at it from behind.