So, following my rant thread a few days ago (here, in case you haven't seen it), my friend and I decided to do some research to see what exactly can and can't push a Trojan back if he's facing you. We did did a couple days ago but I've been too busy and lazy to make this thread until now. Oops :p

Anywhoo, we tried a variety of commonly used weapons and shields, as well as the Sprites' abilities and even the Barriers we can pick up and use, and got various results. We tested this in the Blades of the Fallen mission because it was quick to get to the Trojans and we could get ourselves cornered by them and have more than enough time to try to escape before getting killed.

Now, let's start with the results. Shields first, since most Knights' instincts is to Shield Bump.

~> Proto Shield: The first shield we get in the game. Obviously, it doesn't push the Trojans at all.

~> Swiftstrike Buckler: Don't even bother. Just like the Proto Shield, it does nothing to the Trojan.

~> Volcanic Plate Shield (and possibly other Plate Shields): This one pushes Trojans back a bit, definitely enough for you to escape. If you have two Trojans cornering you, though, you might need some luck so one isn't pushed into the other and keeps you trapped.

~> Crest of Almire: A bit less unf than the Volcanic Plate Shield, but still enough for you to escape one Trojan (again, you might need luck to escape two).

~> Grey Owlite Shield: The same as the Crest of Almire.

~> Dread Skelly Shield: The same as the Volcanic Plate Shield. It actually surprised me.

~> Barbarous Thorn Shield: Same as Crest of Almire

~> Exalted Honor Guard (and Aegis): Nothing. It doesn't push the Trojans back at all.

Those were the shields we tried out because, like I said at the start of the post, they're the ones we use / see others using more often.

Now for the weapons.

Swords

~> Voltedge (And other 5 star Brandishes, we assume): Normal swipes do nothing. A charge attack sometimes pushes the Trojan back. From what we saw, it only pushes the Trojan back after he attacks.

~> Final Flourish: Normal swipes do nothing. Charge attack also seems to do nothing.

~> Barbarous Thorn Blade: Normal swipes do nothing. Charge attack, despite being a projectile attack, seems to do nothing. Since the charge attack has a swipe like the Brandish charge, though, it might manage to knock the Trojan back a little after he attacks.

~> Divine Avenger (and Gran Faust): Despite having quite a bit of knockback against other enemies, Trojans just laugh in your face.

I think that's it for the swords we tried.

Guns

This is where it got weird. Sometimes the Trojans would be pushed back but other times they would just stay in place then attack us.

~> Argent Peacemaker (and probably Sentenza and Obsidian Carbine): Some shots managed to knock the Trojan back. With luck, you could certainly make it out.

~> Valiance: Same as AP.

~> Polaris: Same as AP. If you can charge it, you can easily push the Trojan away, though.

~> Hail Driver (and probably other Alchemer guns): Same as AP, but since you only have two shots instead of six, you might get your head smashed during a reload.

~> Blitz Needle (and probably other Autogun lines): Same. Some shots could push the Trojan away, others did nothing. A charge could keep him from attacking even if it didn't push him away. The fact that you need to stay still while shooting it might work against you.

Bombs

~> Nitronome: Surprisingly, the Nitronome does NOTHING if the Trojan is facing you (and, as such, the center of the bomb). I was actually disappointed by this.

~> Big Angry Bomb: This, on the other hand, was the thing that sent the Trojan away the farthest, from everything we tried. But let's admit it, no one carries the BAB frequently because of the Movement Speed Decrease during the charge and because of the slow fuse.

~> Deadly Crystal Bomb (and probably all the other Shard bombs): Nothing. The first detonation did nothing, the shards' explosion also did nothing. I don't think many people carry this around anyway if they have a Nitronome and Dark Briar Barrage. Speaking of which...

~> Dark Briar Barrage: As expected, it did nothing to help us.

That's it for weapons. The only viable one was the Big Angry Bomb. All other weapons were either useless or unreliable and luck based.

Let's move on to the Sprites, shall we?

Seraphynx: Both of the Seraphynx's offensive skills (offensively borked, if you ask me), Dazzling Light Ray and Disintegration Ray, were useless.

Drakon: We don't have any Ultimates on our Drakons yet, but the normal Firebolt worked like the guns: sometimes it pushed the Trojan away, other times it didn't. The Flame Barrier was also useless.

Maskeraith: The Quills skill seemed to work like the non-charge attack of an Autogun: some quills managed to push the Trojan or at least interrupt its attack, but other quills did nothing at all.

The Shadow Cloak should help if you're the only one cornered. But since we did this research because the two of us got cornered by two Trojans, it's safe to assume that the Cloak would be useless because the Trojans would just target your trapped friend instead.

Last, and probably least, the usable Barriers. They were mostly useless. Sometimes they would magically inflict their status on the Trojan that was trapping us, but it had no knockback.

So after all that, we reached the conclusion that SKs knockback mechanics are really weird, at least with Trojans. We were also surprised at how some of the weapons/shields seemed to help (or fail to help) when in that particular situation.
The best advice is to always be on your toes around Trojans and avoid letting them trap you in a corner. If you do get cornered and killed, pray that they'll move away before the Emergency Revives gets you back up, otherwise you'll most likely need to use a Spark of Life to knock them away.

A little Edit after posting this: If you're in a party where you see one or more of your party mates trapped by a Trojan, do attack them as fast as possible so they don't smash your party mate to little bits!

Moar Edit: Added Sealed Sword results.