Nardole is a cybernetic companion of River Song and The Doctor, first introduced in the Christmas special "The Husbands of River Song". The Doctor later "rebuilds" him, prior to the events of the Christmas special "The Return of Doctor Mysterio"; suggesting Nardole is primarily robotic, as such a feat would not normally be possible with an organic being.
In Doctor Who S10E5, "Oxygen", we find The Doctor, Nardole and Bill on an oxygen-void space station. Throughout the episode, the trio are faced with challenges involving the lack of oxygen. Notably,
The three have to put on smart suits in order to receive oxygen, after the room containing the TARDIS is sealed off, and the additional oxygen vacuumed out into space.
One thing seems to stand out, to me. Nardole is a robot; and yet, he appears to be just as concerned with the lack of oxygen. This is especially highlighted, later:
Bill's space suit malfunctions, while they are waiting to be let out into general space, and removes her space helmet. In order to save her, The Doctor gives her his helmet. As a result, he goes blind. This is no light scratch - he is still blind at the end of the episode.
In contrast, if Nardole does not actually require oxygen, he could simply have given her his helmet. At the very least, his robotic body would not be as susceptible to the vacuums of space as The Doctors organic body.
If Nardole is robotic, why is he so concerned with having oxygen?