The Trashmaster Title – Secret Title
The Trashmaster Title is a character-bound hidden title added in the Battle for Azeroth expansion. You can permanently unlock the title by completing a few tasks for Jani.
Step 1: Get the cloak: Trashmaster's Mantle
You can use a Seal of Wartorn Fate for an additional chance to get the cloak when defeating K.U.-J.0. on Mythic difficulty.
Step 2: Complete the achievement: Get Hek'd
To complete Get Hek'd you will have to complete a number of tasks for Jani in Zandalar.
For more info on how to complete this achievement you can check varenne's comment: https://www.wowhead.com/achievement=12482/get-hekd#comments:id=2570573.
Step 3: Find Jani
Horde players can find Jani at 35.4 7.7 in Dazar'alor.
Note: Make sure Jani is not your active Loa. You can change your active Loa by talking to Chronicler Ash'tari at 50.7 35.3 in Dazar'alor.
/way Dazar'alor:Zuldazar 35.4 7.7 Jani
Alliance players can find Jani at 36.2 36.8 in Vol'dun.
/way Vol'dun 36.2 36.8 Jani
Step 4: Speak with Jani
Speak with Jani and complete the quest "I Am the Trashmaster" by giving her the Trashmaster's Mantle cloak.