Answer 1

{PHP + SQL Query with database knowledge
bonus
//Server knowledge

Answer 2

PHP language is now used for smaller projects because other web frameworks like ruby on rails, django have taken over. Although facebook still runs on php but it has incorporated new tech to meet up with the advancement. I usually advise people to broaden their knowledge and not to focus on learning php only. it's not enough to be an efficient backend developer. I hope you found this useful.