同学你好，该知识点来自沪江网校《新概念英语1、2、3、4册连读【周年庆特惠班】》的课程，想要更系统的学习，欢迎进入课程学习。不仅可以和更多的同学一起学习，而且还有老师、助教随时的学习指导和知识点解答哦。

同学你好~
Then he and his fiancée, Jane, went horse-riding, after which Jane cooked their dinner in the microwave oven
这里which引导一个非限定性定语从句，指代的是前面整个主句，也就是Then he and his fiancée, Jane, went horse-riding这件事
after which指的就是在这件事之后。

类似的比如
Please stand and pledge the flag, after which Dr. Jerome Taylor will give the invocation.
请起立对旗宣誓，之后杰尔姆·泰勒博士将做祈祷。（which指代Please stand and pledge the flag）

可以在这里复习一下非限定性定语从句的用法
https://www.hjenglish.com/new/p1286218/

祝同学学习进步~