https://www.gamespot.com/articles/caydes-will-how-to-get-ace-of-spades-in-destiny-2-/1100-6461808/

If you've paid even a little attention to Destiny 2: Forsaken, you probably know that it's the death of your pal Cayde-6 that kicks off the expansion's events. Early in the Forsaken campaign, you'll find Cayde's Will sitting in the Pursuits tab of your inventory. It's this item that guides you through the steps required to find and repair the Exo hunter's exotic hand canon, Ace of Spades.

The Ace of Spades is a powerful weapon that can bring down hordes of enemies in PvE and deliver tons of damage to opponents in the Crucible. It's definitely worth getting, even though completing the quest steps is no easy task. Here's a rundown of how to complete each step.