This line refers to Monygham as the Devil; see earlier when Nostromo conflates "enemy of the people" and "tempter" , and earlier still where "tempter" refers specifically to the Devil. As a question about Dr Monygham it is fairly meaningless, except to add to the sense of alienation surrounding Nostromo's death. Relating to the Devil, however, the question has a larger significance befitting the last words Nostromo is to hear.

Is the Devil, as the ultimate cynic, an enemy of the People? Is the man who awakens Mankind to the cruelty of their institutions and the inaccessibility of their own ideals -- an enemy? Or would not greater harm be done by allowing the dream-ideal to continue, spurring one group to fight another "with their own weapons" into a blood-soaked eternity in the name of a reform that is never achieved? It is this question that Nostromo answers with his "glance of enigmatic and profound inquiry."

Monygham, and the Devil, are not the only ones trying to expose these fatal truths about mankind here. Conrad is, too. The photographer's question might just as well name him and his book, and Nostromo's open eyes might be posing it back again to a wider, ongoing audience. Who is "the weird figure perched by his bedside?" Is it Conrad? Is it you?