Emmie's info is perhaps a tiny weeny bit out of date. There is no poetry reading, these days. Nor, indeed, is there very much in the way of group discussion. At least, not on things like social issues.
The first part - the paper sat in the lecture theatre - is probably much the same as it was before. Besides a multiple-guess section there is also a grammar correction-type section wherein you need to be able to describe (using appropriate meta language) what's wrong with a passage. The paper is (these days, at least) designed in a very similar way to the LPAT.
Passing this paper isn't enough. HKU gets many more applicants than it has places to offer, so there's an interview/group interaction stage. This begins with another error identification and explanation task. Once finished, the candidates are quizzed on the paper and on their understanding of the errors. They are further quizzed on how they would teach certain ideas or parts of grammar, or how they would address such errors if they were to come across them in a real school situation. Candidates should also expect to be asked to expand upon their background and their motivations for joining the course. There isn't a huge amount of actual group interaction, these days, though of course this will depend to some extent on the individual examiner.