If I recall correctly, these kind of exams are generally similar in format to scholarship entrance exams, in that it's not really testing depth of knowledge, but rather reasoning and applying knowledge. At a year 9 level, they're not going to expect advanced trig or calculus, but they might test things like index laws, basic linear functions, basic triangles in terms of maths, or abstract reasoning (like seeing relationships between objects) etc.
It would be worth looking at selective school admissions exams for things to expect (try to look at some of the posts here (
Selective Schools Admissions Tests)
But I wouldn't worry too much, especially if it's an in school test- if you're keeping up with schoolwork, you'll be fine, and even if you flunk it completely, there are always ways to do what you want in the future.