应该是后置定语.
1.修饰名词的成分叫定语.这句
"going instinctively to the heart of a matter"在 this knack 后修饰 this knack ,所以为后置定语.
2.主语补足语必须有两个条件:
(1)句中的谓语动词必须是及物的,后跟宾语+补语;
(2)主语补足语必须出现在被动语态的句子里,主补其实是被动语态的宾补.如:
I kept the baby sleeping.这里sleeping 是宾语the baby的补语.
但变被动语态后,
The baby was kept sleeping by me.这里 sleeping补充说明主语 the baby ,成了主补.