Is it permissible to complete a course of study that involves reading books containing shirk (polytheism/idolatry), atheism, and obscene sexual descriptions, with the aim of teaching the English language and obtaining better job opportunities?

There is no harm in studying the English language to teach it in Muslim countries. There is also no harm in reading stories and novels that contain atheism or sexual descriptions, provided that the heart detests them, and that their content is not narrated in an exam, on the condition that they are not approved of or praised, that the narration is from someone else, and that you are not affected by what you read.