In case you've read the solutions written for the non-GotY version, I found that the killing blow from a deflected arrow seems to not unlock for me (I think some of the GotY achievements are a little "twitchy" compared to the normal version), but I found that only
damaging the enemy with deflected arrows counted, while if you batter them first to lower their health wouldn't count...
For areas with bandits that have crossbow men with them I headed to the north-east area of Novigrad, finding several camps there
If you've not read the others, then kill all of the melee guys first, leaving only the crossbow guy (preferrably 1, as twitching for more can be difficult), make sure you're close enough that Geralt responds as if you're too far away he won't parry and will just be hit by the bolt... tap
just before it hits you, similar to a parry, and it'll deflect, but ensure you have the deflect skill purchased, and it's active in your list
For timing, I found that waiting for him to raise the crossbow, then tapping the button JUST
after (a fraction of a second), but your timing may vary depending on your response speed - while I only do this when I'm killing time, it's a LOT easier & faster to just carve them up with your sword, so I only deflect when I was going for this achievement