in which 是定语从句,修饰 the year,原本是
...the year which each person joined the club in
最后那个 in 前置到 which 之前,变成了 in which,在哪（年）
整句话的意思是：
还应注明所拥有的狗的品种,以及每个人加入俱乐部的年份