这个是 sth happen to sb 的句型 , happen to sb指发生在某人身上
"sth.+happen to+sb."意为"某人出了某事(常指不好的事发生在某人身上)"。例如:
A car accident happened to him yesterday.昨天他发生了交通事故。
What happened to you?(=What was wrong / the matter with you?)你怎么啦?
所以happen to 是在“ What happen to Jack at home? ” 里是固定的搭配,而不是分开 happen 跟 to jack ...
jack 主语
to 没什么语不语的
宾语补足语