Hello aspirant, 

In the first place, solved papers / previous year papers of JAM Mathematics Exam are highly important

The syllabus is ,

Sequences and Series of Real Numbers

Functions of One Real Variable

Functions of Two or Three Real Variables

Integral Calculus

Differential Equations

Vector Calculus

Group Theory

Linear Algebra

Real Analysis

As can be seen, there is no dearth of books for IIT JAM Mathematics exam. Actually, there are too many books.

Select one or two books for IIT JAM Mathematics exam preparation per subject. Do not overload your brain with learning theoretical proofs; nevertheless understanding of those is vital to remember formulae. If a particular book you prefer has more of theory, do refer another for practice questions