As you want syllabus of ONGC Graduate Trainee Entrance Exam, so here I am providing complete syllabus:

ONGC Graduate Trainee Entrance Exam Syllabus

FOR ELECTRICAL
Network Theory.
Power Electronics & Drives.
Estimation and costing.
Power Systems.
Utilization of Electrical Energy.
Analog and Digital Electronics.
AC Fundamentals.
Magnetic Circuit.
Electrical Machines.
Basic Electronics etc

FOR INSTRUMENTATION
Transducers.
Analytical, Optical, and Bio-medical.
Analog Electronics.
Digital Electronics.
Control Systems and Process Control.
Electrical and Electronic Measurements.
Signal and Systems.

FOR ACCOUNTS
Indian Audit and Accounts Service
Taxation
Business Economics and Indian Economics.
Business Laws, Auditing
Principles and Practice of Management
Cost and Management Accountancy

FOR COMPUTER KNOWLEDGE
MS Office.
Windows.
MS Excel.
MS PowerPoint.
MS Word.
Internet Usage.

FOR APTITUDE
Number Systems.
Percentages.
Averages.
Mensuration.
Use of Tables and Graphs.
Computation of Whole Numbers.
Ratio and Proportion.
Interest.
The relationship between Numbers.
Discount.
Profit and Loss.

FOR REASONING
Analogy.
Number Series.
Problem Solving.
Clocks & Calendars.
Non-Verbal Series.
Logical Sequence of Words.
Cubes and Dice.
Visual Memory.
Decision Making.
Arithmetical Computation.
Coding-Decoding.

Here I am suggesting you for best books for ONGC Graduate Trainee Exam for your reference:

ONGC Graduate Trainee's Exam Mechanical Engineering Paperback – 2015
by Chandresh Agrawal (Author)
Rs. 333/-
Paperback
Publisher: Priyanka Prakashan; Second edition (2015)
Language: English
ASIN: B00KDEOSMY

ONGC Graduate Trainee's Exam Executive (E-1) Paperback – 2015
by Chandresh Agrawal (Author)
Rs. 240/-
Product details
Paperback
Publisher: Priyanka Prakashan; Third edition (2015)
Language: English
ASIN: B00KJFFAO2

Management/Executive Trainees : Electrical Engineering Recruitment Exam Guide (APPRENTICE ENGINEERS/GRADUATE ENGINEERS TRAINEES etc.) Paperback – 2017
Rs. 363/-
Product details
Paperback
ISBN-10: 9386298325
ISBN-13: 978-9386298324

Management/Executive Trainees : Electronics & Telecommunications Engineering Recruitment Exam Guide (APPRENTICE ENGINEERS/GRADUATE ENGINEERS TRAINEES etc.) Paperback – 2017
Rs. 428/-
Product details
Paperback
ISBN-10: 9386298309
ISBN-13: 978-9386298300