If you're gearing alts during Midnight pre-patch and need trinkets, consider the Nightfall event in Hallowfall

I've been gearing up alts to try the Mage Tower challenge. The pre-patch event in Twilight Highlands provides for all slots except trinkets, so I've been looking elsewhere.

The Nightfall event's weekly quest The Flame Burns Eternal awards a Radiant Service Satchel which (among other things) contains 1 Radiant Emblem of Service which can be used to purchase a choice of Adventurer 1/8 trinkets. When upgraded to Adventurer 8/8, these are item level 118, quite close to the 120 cap for the Mage Tower challenge.

• Arathi Minister's Receptacle (notably, this trinket is NOT unique-equipped)
• Baleful Excerpt (you can switch this trinket's suffix):
  • Baleful Excerpt on Dark Summons
  • Baleful Excerpt on Sacrificial Rituals
  • Baleful Excerpt on Prophetic Death
• Hallowed Tome (you can switch this trinket's suffix):
  • Hallowed Tome of the Abbot
  • Hallowed Tome of the Zealot
  • Hallowed Tome of the Crusader
  • Hallowed Tome of the Cleric
• Shadowed Essence
• Shining Arathor Insignia

To unlock the weekly quest, you need to complete the breadcrumb quest A Radiant Call which can be found in the Suggested Content section of your Adventure Guide.