This is Drack's loyalty mission. Finish up the mission he gives you regarding Kadara/Spender first and inform him and the Alliance of Spender's treachery. This will unlock Drack's loyalty mission. The mission is titled "A Future for Our People" and it is located in the Krogan colony.
I will not spoil the details of the mission. Like Vetra's, it's pretty straightforward. You'll have two mechs to fight at the end so if you're playing on Insanity, play it safe. When you finish the mission and arrive in the greenhouse, you'll have a conversation with Drack about his thanks, and you'll get a black screen saying you have unlocked Drack's Level Six abilities. The achievement will then pop. Happy hunting!