Rock the Casba is a main quest given by Sergei. It is received after the NRG hack quest.
Boris tells you that he and Sergei have tracked down the mayor to one of two locations, Rookwood town Hall or the Casba Factory. He asks you to meet up with Sergei on the outskirts of Rookwood in order to proceed.
Make your way to Sergei he will tell you that he will hit the town hall while you hit the Casba factory. To get there, follow the gravel path immediately outside the house until the end of the path.
Once there, bust through Security and discover the mayor just left. Talk to the Foreman to discover this. Then return to Sergei to complete the quest.
Once finished, see Boris. He will send you back to seeing Harry who will reward you with your first ability. You will either be able to entomb someone, gain the hacker trait, throw a fireball or one other spell.