Dear Student,
Glad to hear that you have your interest in making a career in stock market after your 12th, for it I might suggest you to go for B.a. Economics hons as your graduation as it'll give you an overall knowledge about how the economy and stock markets works or you can even go for B.com or B.com hons and after doing your graduation if you want to pursue post graduation I might suggest you to go for MBA in finance and these courses will give you enough knowledge to make your career in stock market.
Hope this might help you.