Following books are the best which you can refer for the exam

"D.El.Ed. Entrance Exam Guide" by RPH Editorial Board

"D.El.Ed Entrance Exam Guide" by Arihant Experts

"General Knowledge and Current Affairs" by Manohar Pandey

"D.El.Ed PET Exam Solved Papers" by Pustak Mahal

"Kiran's D.El.Ed PET Exam Guide" by Kiran Prakashan

You can also refer NSERT for basic concepts.