So an Aether kineticist gains this 3rd level infusion that let's her fling her enemies at other enemies as long as she bypass SR, the enemy fails its Fort save and She hits the other guys regular AC. Now I've got a few questions about the power. First off, since it requires a Fort save, does it work on undead and construct(since they are immune to Fort that don't affect object and it's never specified in the infusion).Secondly, must I always aim at an enemy? Or can I fling him against the wall, or the roof for extra falling damage.
Lastly, if the enemy travels in a direct line toward the target and I have an ally with a greatclub who is adjacent to that trajectory and readies an action to take a swing as the enemy passes. What would the aether-coated flying enemy AC be and how much strenght or damage is needed for a homerun?
If it does not specify that it can target objects, undead are immune to it.
As the spell says. If it says you have to throw it at another enemy, you have to do that, especially if it doesn't mention throwing them against a wall.
Their AC would be normal. Technically you wouldn't be able to move them at all regardless of damage, but an awesome blow combat maneuver could change that...
Couple of things
Foe Throw specifies target but doesn't say enemy. In fact the references to an enemy apply to what you are throwing not what you are throwing at.
Keep in mind that unless you assume otherwise this is just a variant kinetic blast so you can definitely target walls, squares, floors or creatures with the blast.
Foe throw allows you to throw someone instead of something. Given that it normally targets objects and this expands what you can throw I would be inclined to believe that undead and constructs can be thrown, as long as you penetrate their SR and they fail their fort save.
The ability refers to throwing the creature only at 'the target'. At no point does it say you have to throw it at a creature, enemy or foe.
Enemy movement when thrown does not provoke. However, your friend could ready an action to hit it as it goes by, assuming you successfully use the ability.