what specifically are you having trouble with?
to speak as a general outline, what I'd do is spawn the collision sensor based upon the animation frame.
1) character switches to sword swing animation
2) when the correct frame is reached, spawn the sensor actor at the appropriate coordinate relative to the actor (so you'd spawn actor at x of self + offset number and y of self + offset number, the offset being what you use to tweak its location)
3) give the sensor actor a simple block or circle graphic and make it so it can't move, also set it to sensor and the appropriate collision group and so on. have it die after a very short time, after, say, .1 sec or less (depends on the animation though, I suppose)
4) tell the enemy that when it collides with that sensor, damage self (whatever you want your damage logic to be).
that's the general outline of how I'd approach it. is there anything specifically you're having trouble figuring out or need explained in more detail?