CBSE 12th

Alok, your question is little confusing. Why you want to reappear for 12th? You were not having Science subjects when you did your 12th in 2015 or you were having less marks due to which you could not give JEE Mains.
Another thing is go for 12th form NIOS keeping in mind that JEE has age limit so, in case that is something that you won't fulfill after doing 12th from NIOS than don't waste your precious time.
There are many courses available these days to go for.
If you have any passion for computers you can go for BCA or B.Sc Computer Science or B.Sc IT.
If you want to learn the tricks of management or want to start your own business, BBA, B.Com (Professional) can be good choices.
If food and its aroma arouse you, hotel management can be your calling. Or on this line only, you can join a course in tourism and hospitality that is going to take you places.
If you believe in weaving a magic with your words and also have a streak of adventure in you, you can go for BJMC or even Bachelors in Film and TV production.
If you are having a creative bent of mind and you want to show that creativity by making inanimate objects move and talk, you can think of a course in Multimedia and graphics. If you love showing this creativity on cloth and on canvas, then its fashion designing and fine arts that you have an aptitude for. If your creativity lies in making the interiors of a place appealing then certainly you should go for interior designing.
With so many good conventional and modern options available to you, you can make a successful career for yourself by choosing a branch of your choice.
After choosing a course, another important thing is the institution/ university from where to do the course. There are many world class universities with modern infrastructure and highly qualified, experienced faculty who have made a name for themselves in the field of education by imparting quality education.
Not only are they imparting quality education but some like Lovely Professional University, Chitkara, Maharishi Markandeshwar University etc are also offering good placements, etc. Some of them also offer scholarships.
Good luck.