The main questions to ask of any trailer should be as follows:
What type of trailer is it?
1. A teaser?
2. Theatrical trailer?
3. A TV spot advertising the film on release?
What is the film's USP? ( Its unique selling point?) In other words how are the distributors positioning the film in the marketplace? Which elements in the film's genre is the distributor highlighting which sets the film aside from other films in its genre.
What are the messages in the film's trailer and what do they say about the film?
Remember that the type of release ( wide, limited, universal ) and the date of release will have been carefully planned to maximise potential audiences.
In the media studies and film studies exams all you need to do is be able to write a paragraph or two on the posters and trailers of your case study production company's film so you can argue how the distributors tried to market the film.
Here's a good link to practice with film trailers for films currently on release.
The link to Frank Baker probably has more than most students would need.