While the knockback effect works on PCs, through my testing, they currently don't work on NPCs. It also only pushes in one direction, which is unlike live knockback.
I have extensive experience with knockback effects from playing my Bard on live. There are two mez songs that the Bard gets in his career and one produces a push, and one produces a pull.
To clarify how knockback effects work for those that may not remember, it always pushes directly away from the caster (in the direction they face), or directly toward the caster (opposite of the direction they face), depending on whether the value is push (positive) or pull (negative).
I remember this specifically because I would use that to my advantage to separate mobs and also keep them from falling off of cliff edges, i.e. Royals in Sol B, etc.
The above example spells are:
Sionachie's Dreams which has a value 2 knockback.
Song of Twilight which has a value -4 knockback (pull).
I believe these push/pull features were integrated to help separate mobs from each other since Bards didn't have an AoE mez of any kind (until Creeping Dreams that is), to make targeting a bit easier.
Anyone have any ideas on how to go about fixing this?