Your number one is the best of the three.
Numbers two and three are not, I suggest, common idioms. Number three is close, but it would sound better to my ear if it were
"What job do you intend to have after graduation?"
An occupation is not usually thought of as something you have, but something you are or were or hope to be.
"My occupation is dentist."
"Her occupation at the time was administrative assistant."
"What do you hope your occupation will be after graduating?"
As for your number two, I suggest you re-word it as follows:
"What job will you look for after graduation?"
While it is OK to say "I took the job," or "I will take the job if they offer it to me," it's not common to say "What job will you take?" Better is "What job will you look for?" or "What job did they offer you?" or "If you take the job, what salary will you ask for?"