he has got quite used to what people say about him.

这是get used to sth “习惯某事”句型,what people say about him 是由what引导的宾语从句,语法功能相当于sth,做介词to 的宾语,其中引导词what兼做say的宾语.不能用people say about him或people say about him what 代替.
再问： what还原回去的位置是people say what about him是吧？ 单独说people say about him语法对么
再答： 逻辑上是，people say what about him。单独说people say about him语法不对，是病句。 【俊狼猎英】团队为您解答。