不是代词，whether是连词，意思是是否，例如：

1、Whether we need more food depends on how many people turn up.我们是否需要更多的食物，这要视到场人数而定。

2、I asked whether they could change my ticket.我问他们是否可以给我换票。

3、Your lawyer can advise you whether to take any action.你的律师可以告诉你是否起诉。