I put this in the Guardian Section, but really it goes for warrior too and any other class that can jump to and has a knock back. I hardly played any melee, since I feel melee like in most games is fun to play but underpowered, but that isn't my question. My question is first can you in a siege of a keep, can you use one of the jump to / warp to abilities to jump to an enemy and then use your push back to then knock the player off the wall?

My example is say we are at a castle and we have it under siege and there's a player on the oil or any siege equipment. Is it possible for me to jump to the player or someone by him in LOS and then use my knock back to then push him off the wall into our group on the ground? That would one stop him from being rezzed so easy and 2 it would stop the siege equipment from being used at least for a short time. Also, if it was a bigger area knock back like the guardian has could knock multiple defenders from the wall.

I never saw anyone doing something like this during any of the WvWvW I did. I'm curious if  no one thought of it, I missed it all together or because the game has some mechanics in place that stops this from being possible.

Again this could work with any class that has a jump to and a knock back.

P.S. This could substantially change what class I play come launch and change my opinion of the melee classes. Also, I have seen people talking about the Guardian having a pull to ability and I can't seem to figure out which ability or combo of abilities allows for Guardians to pull players to them. Thanks ahead of time for any answers anyone could give me on all or any of these questions I have.

The only class that was able to make it to the top of a wall was Thief with shortbow which I'm certain was unintentional.  The game is pretty determined to prevent players from using abilities to cross gaps or reach places that you are unable to run/jump to.  With certain leap abilities, like the Guardian's greatsword ability you can cross small gaps that are not jumpable, however.

As for knocking people off of walls that is definitely possible and I have done it.

However, just because they're dead on the ground outside of the keep doesn't mean they're out of the fight.  Most of my time spent defending keeps on my Guardian involved me jumping down with another group of melee fighters, skirmishing the enemy quick, reviving some people, then all falling back into the keep.  Heal up, rinse, repeat.

This ^.

Though in Spvp matches I did notice that the guardian teleport "Judge's Intervention" was very liberal in weather or not it allows you to use it when a target is on a platform above you.

As long as the ramp up to the target is less then 1200 units away and not blocked off to you (you couldn't just run around and take it anyway) it will allow you to teleport to them.

Sadly this won't work in WvW vs enemies on walls unless the gate is already down.

Well that sad, but that is what I was getting at. Thanks for the answers guys.

How about the ability for Guardians to pull player to them? Do they get that? If so what is it called? and Will it work to pull people off the walls?

It's a Greatsword ability and it functions the same way as teleports/jumps.  There needs to be a clear path for them to be able to move to you or it won't work.  Not to mention the distance you'd have to be from the wall to not be obstructed by it would make you out of range.