Retired but now in training as a bus operator. Have gotten two paychecks, but I don't graduate officially for one week from now. What is my job occupation?

You can enter Retired.  This is only used for statistical purposes so you could enter Bus Operator if you want.

You can enter anything you want.  Occupation is not important.  

The IRS only uses "occupation" for statistical purposes.  It is not used for anything that will affect your refund or tax due.  Since you were retired for 2022, and have not yet begun working as a bus driver, it seems like "retired" would make sense for 2022.