The "Detonate Grenade" quickhack can be bought from a Netrunner vendor in Batty's Hotel (Pacifica, Coastview) for $4500
After the purchase fast travel to Pershing ST (Watson, Northside) then mark the nearest drop point (The one southwest) and walk towards it, once there is 100m left to the drop point look to the left and you will see 3 enemies near 2 cars, scan one of those enemies and use the "Detonate Grenade" quickhack on him (Be sure to have an operating system that has quickhack on it) and then just wait a few seconds and give time for the quickhack to kill those guys.