On this page of our game guide to Batman: Arkham Knight we explain how to meet with the Oracle on the Clock Tower. Batman must climb the tower and find an interactive chest piece.
To continue the main story, you need to leave GCPD. The only exit in the building is located in the eastern part and it leads to the parking lot, where you've parked your vehicle.
Enter the Batmobile and head to the Clock Tower. As you go, Lucius Fox will contact you and you will learn that the booster is now available for use. When you reach the Clock Tower, leave the Batmobile and use the hook to get to the top. Press the key/button responsible for interaction to get inside the Tower. Now, switch on detective mode and locate a bust, which is also a scanner. Approach the Batcomputer and use it. Watch a cut-scene about meeting Oracle.