Does the amulet of healing heal all damage, stamina, and remove all poison? Or does it heal just wounds and stamina? Or does it heal an amount equal to your max health? Or does it heal an amount equal to the difference between your maximum and your current health?

Amulet of Healing says: Restore your wounds and fatigue to their maximum values.

So the final state of the hero is defined: He has max. wounds and max. fatigue after using it. That part is clear IMO.

Poison says: If the hero later receives healing, these poison tokens are removed first, one token per wound that would otherwise be healed. Once all of the poison tokens have been removed, the hero's wounds can be healed normally.

So when restoring to max. wounds you remove poison counters until you actually can start adding wounds until max. At least that´s my reading.

Since Poison uses the term "healing" and the Amulet "restores wounds", one could make a point that the Amulet ignores Poison and the hero would end up with max. wounds, max. fatigue and the poison tokens still on him. But the term "healing" is not really defined differently and only used in the context of healing potions and poison in the base rules, so my guess would be that "healing" and "restoring wounds" are used synonymously.

I agree with Parathion's interpretation.