Two questions about this gem.
1. If I have it equppied does my part benefit from it?
2. Can a follower proc it?
1. Yes party members benefit from it
2. No your follow can not apply the debuff or dot (legendary gems don't work on followers)
My Twitch Channel
All legendary gem effects cannot be proc'ed by followers.
I thought Bane of the Trapped was affected by Follower spells? Stuns/slows etc? Of course this pertains to you wearing the gem, not them, but they can proc your gems to a degree?
WD Season 8 https://www.diabloprogress.com/hero/finiar-1655/Kildare/84509816
Monk season 7 http://www.diabloprogress.com/hero/finiar-1655/MojoJoJo/42225505
DH season 6 http://www.diabloprogress.com/hero/finiar-1655/DeadShot/75655606
Angry Chicken http://www.diabloprogress.com/hero/finiar-1655/WhoDoVooDoo/68187610
What? Me worry?
If you are wearing BotT, it will work on any slowed target regardless of who slowed them, be it yourself or your follower or other party member. That's just how the gem works, not exactly follower proccing it.
It's also proc itself if u didn't know