I'm a huge nerd when it comes to history. So I had a wide range of questions to debate over but ultimately went with; 'To what extent is ‘the Final Solution to the Jewish question’ the worst act of genocide in human history?' I did well with this, although I also wish I went with other topics such as politics, computing, artificial intelligence, war etc. Just pick any topic you know you enjoy (ensure it doesn't overlap with your studies), find some preliminary source material and go from there and you'll be fine!