I want to make a sword that does no knock back

The only way you'll be able to achieve this effect is by giving the other players/mobs the knockback resistance attribute modifier.

This is possible from what I understand, and I think it's actually a modifier to the sword. I'm not going to dig into it right now, but it may be possible.

A knockback of 255 could be the solution, because that is equivalent to nothing in most cases, but I don't recommend trying it in case it does launch you 29,999,999 blocks out.

Items will always do knockback because all mobs have the ability to take knockback. If you uses any item (even your fists) and hit a mob they will take knockback. Therefore like Snafu_ said, it will be impossible to accomplish such a task with any item (not only a sword) unless you modify the mob taking the knockback (like adding a knockback resistance attribute).

I believe if you get a sword with knockback 10,001 (With commands) then it will go into minus knockback. I haven't tested this myself so I am unsure if this method works.