The dank corridors of Torghast are yours to explore in World of Warcraft: Shadowlands. You’ll eventually unlock each wing, which will rotate on a regular basis, allowing you to complete runs for Soul Ash and give you the chance to build your legendary armor. Before you get there, you’ll need to finish the Torghast storyline, and that includes a quest called Finding a Witness.
After you find Jaina Proudmoore, Finding a Witness will be the next quest in the story chain. You’ll need to wait until the following weekly reset; although Blizzard has removed some of the time delays for the Torghast storyline, Finding a Witness still needs a reset to appear once you have completed the previous quest.
When you pick up the quest, you’ll need to look out for Captive Dredger throughout the layer of Torghast. You can complete this on any layer during your run of the tower, but it’s obviously easier if you locate them early, before getting too deep into the tower.
After you locate Dredger and speak to him, you can proceed through Torghast as normal, or exit the tower and turn in the quest to Highlord Bolvar Fordragon back in Oribos. The next quest, Lets the Trail Go Cold, will need to wait an additional week before everything resets and you continue the Torghast storyline. Once you reach the end of the story, you can try your luck on the Twisting Corridors, an even more challenging version of Torghast.