She knows of a shop

She knows of a shop _______ you can buy things like those.
-- Dad,where can I buy some writing paper,envelopes and stamps?
-- Ask your mom.She knows of a shop _______ you can buy things like those.
怎么划分回答的这句句子成分?那个of是怎么回事?为什么用where而不用which?

-- Dad,where can I buy some writing paper,envelopes and stamps?
意思：老爹,哪儿可以卖到信纸,信封和邮票呢?
语法分析：DaD,独立成分,名词作呼语.
where 作疑问代词,进行半倒装
I 主语
buy some writing paper,envelopes and stamps谓语,其中BUY及物动词,后接直接宾语,some writing paper,envelopes and stamps
下一句
-- Ask your mom.She knows of a shop _______ you can buy things like those.
意思：问你妈去,她知道有家店可以买到你想要的这些东西
语法分析.Ask your mom祈使句,
She主语
knows of 动词短语,
a shop宾语
_______ you can buy things like those.作同位语,所以选WHICH,
所以选WHICH,
我的回答.我是英语教师,有问题问我