Best to check the Modern History Syllabus for what topics are covered in the preliminary year. Although there is a CORE that looks at the causes of World War I, and also a unit which is entitled the student's 'historical investigation' - this is just a big assignment that the student undergoes for roughly a term. Usually schools opt to do 2 case studies (though some do 3, depending on how long they spend on the historical investigation). If you look at the syllabus there's a range of case studies that the teacher can chose from, usually it is up to the teacher as determined per what they like and the resources they have. The Historical Investigation is entirely your own choice of topics.
If you are worried about if you're going to like the topics. Best to ask / email the teachers about what topics they generally teach from year to year. Or even ask a past student, as teachers generally stick within their comfort zones. n_n
And there is no prior knowledge that is to be known. Though you will go over (again) source analysis, though perhaps in more detail - primary / secondary, usefulness, reliability, perspectives, so effectively evaluating sources.
