the two hours'shopping语法请帮看下

这种表达应该是不太对的.
首先,单单看语法结构.two hours'作为定语,主语是shopping,这里谓语用were就有问题了,针对shopping的谓语,应该是was.
其次,从句子要表达的意思入手.这里要表达的意思应该是:两个小时的购物时间有点短.用shopping做主语是不合适的,我们用short来描述shopping,short是用来说时间的.所以建议表达方式如下：Two hours for shopping were short.主语是时间"two hours".
针对你的两个问题,总结如下：
这类表达有两种方式.
一种是a two-hour trip,a three-day journey这类的表达,注意这里是hour,day是不加s的,前面的冠词是要加的.
另一种是two hours' trip,three days' journey,前面加不加冠词都可以的.

一般都说什么 a three-day trip, 类似于 a ten-year-old girl
shopping 作为不可数名词作主语，谓语应该是单数形式，was

Q1. 最好写成 two-hour shopping
Q2. 同上，two-hour trip, ten-year-old boy，不过非考试或是口语上这种说法也么有错

Q1.The two hours' shopping was short.
Q2.不需要家冠词 two hours' trip
three days' journey