Limiting your preparation to a book would not do justice to the exam. However, you can study from the official NMATbyGMAC, 2020 guide in order to gain clarity on the kind of questions you can come across during the exam.
It is essential to give as many mocks as possible and study from any online courses if possible. For your reference, I would list down the broad topics to be studied for the exam here as follows:
QUANT:
Number properties:
1) Numbers
2) Fractions
3) Decimals
4) Calendars
5) Factors and multiples
6) HCF
7) LCM
8) Logarithm
Arithmetic:
1) Percentages
2) Simple and compound interest
3) Profit, loss, and discounts
4) Ration, percentage, and average
5) Time, work and partnership
Algebra and probability:
1) Equations and inequations
2) Sequence and series
3) Permutation and combination
4) Probability
DATA INTERPRETATION:
1) Caselets
2) Tables
3) Bar graph
4) Pie chart
5) Data sufficiency
VERBAL:
1) Reading comprehension: argumentative passages, discursive passages, descriptive passages, analogy based passages
2) Para jumbles
3) Error identification
4) Prepositions
5) Sentence completion
6) Idioms and phrasal verbs
7) Analogies
REASONING:
1) Critical reasoning
2) Deductions
3) Analytical puzzles and input-output questions
4) Other reasoning: missing value in figures, decision making, ranking test, alphabet test questions, Venn diagrams, syllogisms
I would also recommend you to use the material provided on a website that helped me during my preparation:
I hope this helps.
All the best!