Which is the way to get to the post office?哪错了？

没错。
看语境，要不加上nearest,Which is the nearest way to get to the post office?

Which way is the way .....哪条路

Which one is the right way ..........
which 后面不能直接跟谓语，（有些句子可以省略which后的名词）

我自我觉得这样说就可以了
Which is the way to the post office.
你的说法感觉很麻烦。