He was being a doubting Thomas -- someone who does not believe anything he is told.

他疑心很重（a doubting Thomas），这种人不相信所听到的话。

Something was out there, that much was certain, and any doubting Thomas was invited to place his finger on the Scotia's wound.

这是一件真实的事，那是无可置疑的；怀疑这事的人，请他们去摸一摸斯各脱亚号的裂口好了。