Palpatine uses emperor to order a Jet trooper to attack Han. Han and the jet both have triggers "After the attack resolves". If "After the attack resolves" is part of the attack process, the attacker resolves his ability first and the jet trooper gains movement points he has to spend immediately (Since it's not the jet's activation) and can avoid Han's return fire. If "after the attack resolves" is not considered part of the attack process, the player with initiative resolves their ability first.
My assumption is that "after the attack resolves" is not considered part of the attack process and therefore initiative determines the order.