Now that's an open question. Hundreds of interesting topics are CJ related. Global security comes to mind among others.
adjudication,bond, bail bondsmen, court proceedings, defense counsel, electric chair, felony,guardianship's, high security prisons, interrogation techniques, double jeopardy, mandatory sentences, no lo contendre, and many more.
I find interrogation techniques interesting. The skilled interviewer can interpret body language, facial expressions, intonation and voice patterns to help him arrive at the truth. Interviewing suspects is just as much a weeding out process as it is an effort to find the bad guy. An exact science this is not, but, more and more detectives and the like are learning and then employing these techniques to assist them in the search for the truth. Most criminal suspects and defendants want to tell their story and will if given enough time.
Remember too, that criminal defendant's have rights that must be observed by the interviewer and a failure to do so will jeopardize the case.