Depends on which WSET Level 2 you are taking :)
If you're doing the spirits one, then there are a few things to be certain on:
Names of things: regions, categories, processes, parts of equipment.
The choices you can make at each point of production: they like 'which of the following are post-production choices' type of questions.
Numbers: ABVs, numbers of ...
Just go to a supermarket (the bigger the better and I'd suggest Tesco or Asda) and buy their own brand london dry. It's not nice but it's cheap. If you really don't mind the taste, consider vodka instead as it's often a little bit cheaper and essentially the same stuff without the botanicals.
You're unlikely to get it ...