The Augments raised themselves until May 2154, when Malik led them in commandeering a Klingon Bird-of-Prey. They all left the planet, except for Udar, who was deemed inferior by the others. A few days later, Enterprise NX-01 visited the planet to understand more about Soong and the Augments. When the ship left, Udar went with it. (ENT: "Borderland", "Cold Station 12")
The name of this planet was not specified in the episodes (the script of "Borderland" simply referred to it as "a Class-M planet"). However, the planet's name was given in the final draft script of "Cold Station 12". In the same script, Soong's compound on the planet's surface, in 2154, was described thus; "It's a large, single-story structure that resembles a futuristic Quonset hut, nestled in a small canyon with exotic alien flora now starting to overrun the compound."
The Star Trek Encyclopedia (4th ed., vol. 2, p. 417) identified this planet as Trialas IV.
According to Stellar Cartography: The Starfleet Reference Library ("Federation Historical Highlights, 2161-2385"), the Trialas system was located in the Beta Quadrant.