As a non-native speaker, I can share here what I was taught about this kind of questions by my teachers long ago.
In case of "Do you know what his job is", the actual question is "Do you know" and thus it's formed as a question. The second part refers to the information that is supposed to be known, but is not a question per se, so no reason to inverse the verb and the noun, as in a question.
I guess it's kind of khaki of me to respond to problems posted by native speakers
