What is most useful language for a programmer or. A student learning programming?????

Answer 1

http://www.codingdojo.com/blog/9-most-in-demand-programming-languages-of-2016/

Answer 2

I personally recommend Python for students (As that's what most schools teach).

Reading the post below might also answer a lot of your questions.
https://www.reddit.com/r/learnprogramming/wiki/faq