Harrison Jones appears as one of several daily npcs who can visit your garrison. He will offer six quests as part of the Master Relic Hunter achievement.
Fly to Darktide Roost in Shadowmoon Valley and kill Demolisionist Megacharge for his explosives cookbook. He’s located on the south-west end of the island (56.9, 93.0).
The First Ingredient
Continue east, past the buildings and follow the path leading up the hill. The Blasting Powder is hanging off some nearby scaffolding.
The Second Ingredient
Head west towards the the sunken shipwreck in the Evanescent Sea. The High Voltage Detonator can be found just above it (~50.5, 89.7).
The Final Ingredient
Look north-west and you’ll see a path leading up from the water (starts from 47.1, 84.3). Collect blood from the demons in Socrethar’s Rise – the imp packs are easiest.
Breaching the Barrier
Make your way towards the flightmaster’s camp in Socrethar’s Rise. Swamplight Cave is almost directly below it (42.7, 74.2). Carefully navigate your way through the maze without touching any of the runes or arcane barriers. They work just like the trip wires in the Smuggler’s Den (Nagrand) so if you touch them, you’ll be teleported outside. Once you’ve successfully crossed the bunker, loot the Grimoire of the Nameless Void and hearth back to the Garrison.
Hand the quest into Rokhan for your 150G reward.