Go towards the door to Cell Block A. Ignore the inmates kept in the side cells and take the stairs to the lower level of this location. Open the door and start a fight with the first group of criminals. During this fight, you can theoretically limit yourself to the standard blows and counter-attacks (initiate them whenever there appear blue symbols above the opponent's head), but it pays off to attempt more advanced tricks from the beginning of the game, known from the previous installments of the game (e.g. cape swipe, slide or batarang throw).
After you are done dealing with the gangsters, approach one of the defeated opponents that is marked by the game, and press the appropriate key/button to interrogate him. At the same time, you can take a look at the statistics for the fight (the game displays this type of statistics after each major battle).