On this page of our game guide to Batman: Arkham Knight you can find a description which explains how to scan the Cobra tank to discover its weaknesses. You have to identify all weak points and spots of the enemy vehicle in order to defeat it later.
Exit the underground parking garage and carefully approach the Cobra tank, which is patrolling the area. At all cost avoid getting caught in its sight (the blue rays), otherwise Batman will not even have a chance of escaping and will be killed immediately.
You have to scan three parts of the tank - its rear and the two sides. Despite what you may think, it is not necessary to glide or climb on rooftops, as you may well enough approach the machine on foot. In order to scan one of its part hold the key/button as prompted on screen (Batman will inform you whether the scanning was successful or not). After taking three successful scans you will identify the tanks rear as its weak spot.