https://www.gamespot.com/articles/where-is-xur-in-destiny-2-location-and-exotics-hes/1100-6453365/

For the first time since the release of Destiny 2, Xur the mysterious vendor that appears each week selling exotic weapons, armor, and other items, has arrived. This week, the Agent of the Nine can be found on Nessus, hanging out at the top of the map in the area marked Watcher's Grave.

In a change from the first game, an icon showing where Xur is appears on the map and can be tracked to make getting to him easier. Once you're in the Watcher's Grave, look up and you'll find him standing atop a tree. In exchange for your Legendary Shards, he'll sell you the items in the list below.