From Destinypedia, the Destiny wiki

The Risk/Reward Quest is available in Destiny 2. It is situated in The Breach in The Cosmodrome. At first The Guardian has to defeat Dreg variants called Dusk Walker Mechanics to attract three dusk Captains. When all three Dusk Captains have been slayed, The Guardian has to go backwards through the breach and then hop using double-jumps across a series of platforms and pipes to reach one of Cayde-6's stashes, which has the Riskrunner. The Guardian then has to fight more Dusk mechanics, and after they're all slayed then The Guardian has to kill Haviks, Dusk Baron, before finishing the quest.

To access this Quest, The Guardian has to go to the map of the cosmodrome from destinations and find The Breach. (Note: Needs editing from an expert)