Hello there here is the list of recommended build for Demon Tamer as for my knowledge.
Weapons: Staff or Grimoire
Staff: Unholy Staff of the Banished Warlock
this staff is lv95 and from lv95 trial in Dimension of Soul, Dimension Trial - Kahlo Tower: Michelano 3rd boss
Grimoire: Rules of Unholy Truths, Dimension Trial - Kahlo Tower: Seven 1st/2nd boss
This 2 weapons have the ability to lessen the cooldown of your Hellish Foray skill -20%, after using hellish forray, you just have to use Demonfire that will consume 8% of the Boss monster HP when the effect ends.
Gears: if your a new player and doesn't have much stuffs yet you can just use the Vendetta Starter Pack rings, necklace, and cape. For trophies I suggest to use tank trophies there are free trophies when you reach lv80 or 90 if i remember correctly.
For Certificates just use 4 yellows, 2 resists cert, and HP certs
For the Class Talent: Max out Blood Feast first for 20% HP and Demonic Harmony for longer duration of Hellish Forray. The rest of the Class Talents point you have is up to your liking.
All in all, you just need to build you Demon Tamer as a Tank and lessen the cooldown of Hellish Foray and maximize its duration.