Question: how do opposed force checks work?

Ok, in the beta book it describes how resisting force checks works. For example, when Han opposes Darth Vader force grabbing his pistol, Vader would roll a discipline + force move vs. han's athletics.

Ok, but what when the two opponents know the force? Let's imagine Vader trying to grab Luke light saber with the force. What would be the opposing check? Discipline + force vs Luke's' athletic + what? Or would it be Discipline + force vs Discipline because Luke is a force user?

It actually says exactly that (Final paragraph in that side-bar on pg 195). To resist most force attacks in general, it's Discipline vs. Discipline; but for removing weapons, it would be Discipline vs. Athletics. And resisting a Move check that moves the character itself, it's Resilience.

This may sound like it sucks, that you can't use the force to actively resist in these instances, but you can probably use the Enhance power to give you boosts towards Athletics/Resilience. Probably having the enemy rolling their force dice first to see if the roll even can succeed, then using their Discipline as the basis for difficulty, and having the player roll their check against it with their force dice being used for enhance.

I recently read the Bane series, and in the book when Bane is going through his training, one of the first things they teach him is to put up a Force Shield around himself to prevent an opponent from simply pulling his saber out of his hands and cutting him down. I ruled in my game that another Force User would oppose with Discipline + Force v Discipline + Force, the pips on the Force die adding Success or Failures to the Discipline roll. With the Beta rules, I might change it up to Athletics + Force.

But what about when Obi-wan and Anakin were doing their "force bubble of doom" thing on Mustafar? How would that work?

But what about when Obi-wan and Anakin were doing their "force bubble of doom" thing on Mustafar? How would that work?

Currently I don't think it would, but then again whichever one of them was resisting (opinions differ on whether it was Obi-Wan or Anakin that initiated the Force push attack) rolled a few Despair on that opposed Discipline check yet succeeding, so the GM decided to have both of them be affected as a result of those Despair.

Correction: Was re-reading through the Force powers, and the Protect/Unleash Mastery Upgrade would allow the Force-user to bounce a Force power right back at the instigator, provided that the damage is reduced to zero prior to soak being applied.

It'd be a tall order against Move (which would deal 10+successes damage for a Silhouette 1 person), but a bit more doable if that Force "push" was interpreted as being the Bind power in action, with the Control Upgrade to move the target one range band closer or further away.

The force push on Mustafar could also be a narrative thing.

Player 1 Anakin - "I want to use Move to smash my old master into the wall"

Gm: "aah okey, sure"

Player 2 Obi-wan - " Ey, I also want to use Move to smash some common sense in my old apprentice"

Gm: Okey let's do this, anakin, you have the initiative

Player 1 Anakin <rolls dice and succeed> " I hurl

GM : wait just a sec, Obi-wan you can also roll

Player 2 Obi-Wan <rolls dice and succeed> Okay ? What happens, I see that you plan someting?

GM: you keep on dueling when suddenly you both use the force in a great attempt to push each other away but the force pushes against both off you with Anakins raw power and Obi-wans' greater experience in a standstill for a few seconds before you are both hurled into the wall off opposite side of the room.

That might also be an explanation of that scene.