To complete Hard Evidence in Destiny 2: The Witch Queen, you will need to go to the Quagmire location on Savathun's Throneworld and interact with a large pillar.
Interacting with a large pillar will give you a sample to match the Osmic Fragment. That said, the first step in the quest is to find the Evidence board.
Finding the evidence board back in the Enclave will start the Hard Evidence. After starting the quest, fast travel to the Quagmire on Savathun's Throneworld. Once at the Quagmire, you can find the pillar you need to interact with via the location below.
Following the waypoints after tracking the quest will also help you get to the Pillar. Once you reach the area, you will need to find and interact with the Pillar below.
Interacting with the pillar will start an ambush sequence where you must kill ambushing Lucent Brood. Killing the Lucent Brood attacks will progress the quest to the next stage. All you need to do In this next stage is head back to the Enclave and log the Evidence you collected.
That being said, head back to the Enclave by fast traveling to it and find the board as shown above. Interacting with the board will complete the Hard Evidence quest in Destiny 2 and reward you with one Legendary weapon.
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