A leading question is like a trick question. No matter how you answer, you will be guilty of something. For example, "o you still sleep in class?"
If you say "Yes", it means that you still sleep in class. But if you say "No", it means that you used to sleep in class, but you do not sleep in class any more.
The most famous leading question is, "Do you still hit your wife?" If you say, "Yes", it means you still hit your wife. If you say, "No", it means that you used to hit your wife in the past but you do not hit her any more.
Another way to ask a leading question is to ask, "When did you stop hitting your wife?" There is no way to answer without being guilty.