As you have asked about the recommended books for the Oil and Natural Gas Corporation (ONGC) Graduate Trainee (GT) Electrical exam, I am giving you information about it, check below for the details

A Modern Approach to Verbal and Non Verbal Reasoning by R S Agarwal
Critical Reasoning Preparation Guide by Manhattan
Quicker maths by M.Tyra
Quantitative aptitude by R S Agarwal
Competition Success Review
Manorama Year Book
Objective General English by Puri
English Language by Lucent’s General English
Prathiyogitha Darpan
General Awareness & Current Affairs by Manohar Pandey
Electronic principles by Malvino
Network Analysis by M.E. Valkenburg
Engineering Circuit Analysis by W.H. Hyat, J.E. Kemmerly
A Course in Electrical Engineering by Chester L. Dawes, S. B
Design of Electrical Machinery by By William T. Ryan
Electric Machine Design by Henry Metcalfe Hobart
Fundamentals of Heat and Mass Transfer by Incropera, P.P. and Dewitt
Extended Surface Heat Transfer by Kraus, A.D., Aziz, A
Electronic Devices -System & Application by Robert Diffenderfer
Digital Principles & Application by Leach & Malvino
Fundamental of Electric Circuits by Charles K. Alexander
Introduction to Electric Circuits by Richard C. Dorf, James A. Svoboda