Hi Wind, this is because "go over" is a phrasal verb. Phrasal verbs can be confusing to learn at first, have you learned about phrasal verbs yet?

'Go over' is just another Phrasal verb meaning 'to review'. The two words 'go' and 'over' have different meanings when they are used separately and a different meaning when they are used together - it's the nature of Phrasal verbs rather than an implied meaning, it is the meaning! The etymology of the phrase (where the phrase originates/comes from) I wouldn't know. Perhaps you can imagine a person above (over) the job description looking down on it- they are high enough above to see the complete job description, from start to finish.