during which year of my bachelor degree should I appear for GRE??

You can better take the exam in the 6th Semester, in the month of April.Also,it would be more advantageous if you try to appear in that season due to three major reasons:
1.If you are not able to reach your expected score,then you can be able to give a second attempt in the beginning of the 7th Semester (or) before the month of October.
2.As you will be in the 3rd year,there would not be much pressure to think about the Campus Placements and you can peacefully take your exam.
3.Most of the Univerisities start accepting applications from November and also you can be from Campus Recruitments from November(or most probably December),you can happily apply for the Universities after a lot of thought process.