that能不能换成which

能.
但是应该加个逗号.“He has bought the computer,which she likes best." 就是这样,是个非限制型定语从句.如果去掉,主句仍然完整.
which后面是对前面的话进行补充说明的,翻翻书,看看”非限制型定语从句“就明白了.