Occupation is the assignment under which you gain your income. This means that your occupation may be Assistant, IT or anything else, depending on your field of work.
If it says you are a Student, yet you are already working, that is absolutely fine. The occupation is usually taken based on the visa type that you hold, so if you are on a student visa, even if you are currently working, your occupation would be a student. That would not affect anything in your tax filing.