What is the best way to learn all the arguments for and against each possible question?

I know this is a daunting task - and the honest answer is that you can't memorise everything! Don't get too caught up in the details of specific questions, because the liklihood is you'll then end up neglecting many more things than you're learning. Stick to the basics, try and find transferable arguments which you can apply to multiple questions, and above all remember that the quality beats quantity! If you can communicate a single argument in high-level French, you'll impress the examiner more than if you communicate a multi-faceted argument in low-level French.