Question

Where did you get to know her?－－It was on the farm where we worked.为什么不用that，

Answer 1

the farm后面的where we worked是定语从句，不是强调句型。因为强调句型的特点是将It is that去掉是完整的句子。假如是It was on the farm that we worked，如果将It was that去掉，意思变成了“他在那个农场工作”了，但问的是“你是在哪儿认识她的?”。很显然非问非所答。

Answer 2

因为你where之前用的一个地方farm做主语，所以后面要接where...
而that一般用于连接两个句子，本身并没有意思。。。

Answer 3

如果有that 需要加上at
即It was on the farm that we worked at

Answer 4

可以用that.不过这样显得语气特别强烈。是向听者特意强调地点--那个农场。

Answer 5

这里的where就是定语从句的引导词。