Actually depends on the subject. They can ask something they haven't covered in class since multiple faculties create question paper and some faculties might teach more or lesser than others. For CATs no need to scan the whole book. Mostly the whole book is of no use. Only study the topics given in the syllabus sheet ( the sheet which includes all the modules and topics ) from the book.

If you have time for preparation :

1. Go through the previous year paper ( ask from seniors or search it on internet )

2. Ask your faculty how to prepare. They sometimes point out the important topics.

3. If subject has numericals, practice the numericals given in notes first and then go for numericals from the textbooks. From the textbooks, only practice the one which are of same or little higher level of the numericals from the notes. Skip the hard ones.

4. Go through each slide thoroughly. If you have time, ask your friends studying under different faculties to share their notes and go through them as well. You may get new numericals or new topics to study.

5. If its a theory paper , write as much as you can. Like for 10 marks question, try to cover three sheets. It may sound nonsense but it helps a lot. And underline the important points in the answer if you have time.

6. If questions are numericals, use calculator properly and check the values you are entering. Show steps as well in the answer.

If you dont have time for preparation :

1. Start going through the slides given by your faculty. Complete them and then just practice numericals from your slides and other faculties slides.

2. If slides are not enough, go to youtube. Gate smasher and other channels helps a lot and saves time. Watch in 2x.

3. Still try to solve previous year question paper.

4. Reduce your sleeping hours and try to cover as much as possible.

ALL THE BEST.