Best MCQs books for IIT JAM Mathematics
A Complete Resource Manual for MSc Entrance Examination by Rashmi Gupta and Suraj Singh
You should refer previous year papers for IIT JAM Mathematics to analyze type of difficulty level in JAM and practice as many questions as you can. You can even find a set of practice papers in ARIHANT publication (Solved Papers of IIT JAM by Neha Tyagi)
For double and triple integrals, differential equations, and higher order differential equations, it would be best to buy APPLIED MATHEMATICS II by GV KUMBHOJKAR.
You can even find online mock tests for a considerable price and it will really help you.
CAUTION: DO NOT EXPECT THAT QUESTIONS FROM THESE BOOKS WILL BE ASKED IN IIT JAM.
All the very best.