WHICH LANGUAGE SHOULD I LEARN AFTER SQL?

Answer 1

Any language!

As Sql helps with handling Database you can learn Java to do app development with Sql together or you can learn Web development having database ofcourse with html, CSS, Sql, JS etc.

Answer 2

SQL using in all kind of applications : mobile , web, desktop ...ect
so you need to decide what kind if application you want to develop then you think in the programming language