No body knows which factory does he works.

Nobody knows which factory does he work in.
work后面可以加in，LS说的in介词提前也可以。
does后面work应该是原形啊
这种介词不可以省略的，就像I don't know which hotel he live【in】.这种句式里的介词是一定要有的。

要加 in 介词提前

正确的是 nobody knows in which factory he works.

in要的
No body knows which factory he works in .

因为他是在工厂里工作啊 不是work in the factory么！ 当然要in

Nobody knows which factory he works in .

要的，用which提问就要用in,如果是where就不用了，就是Nobody knows where he works.另外宾语从句的从句部分应该用陈述语序，所以正确的说法是Nobody knows which factory he works in.