To get the Inhibitor in the VNC Tower in Dying Light 2 Stay Human, you first have to complete the Broadcast story quest. Once you’ve done that, one of the elevators on the ground floor of the VNC Tower will be activated. Get in that elevator and press 2 to go to the VNC Tower roof.
It’s a long elevator ride to the roof, but once you’re there, exit the elevator and turn left. You should now be getting a marker telling you there’s an Inhibitor Container about 10m below you. There’s a solar panel sticking out of the roof a little way along. Carefully step out onto it and look down to the left. You should see a couple of broken windows a couple of floors down.
It is possible to reach those broken windows using your grappling hook, but any guide that tells you that it’s easier to use the grappling hook was probably written by watching someone else do it on YouTube, and not by actually playing the game. It is much easier and safer to simply drop down and push forward towards the broken windows, so that you land inside. You’re now in the office that contains not only the VNC Tower Inhibitor, but also the VNC Tower safe (and its safe code).