Our teacher has been through this with us theres a fairly good pattern to follow. There's always a question on Parnell and/or land reform in the 1870-1914 section it just comes up in different ways. There's also always a question on Cosgrave and/or DeValera including state building anglo irish relations or the emergency and usually a mix of them and others. We're doing American history and there's always a foreign policy essay and Vietnam hasn't been up in a while as an essay in itself so there's a good chance of it coming up though it may not. 2011 was the last time.
I hope you're doing one or more of these modules so you can use some of that advice