Do you enter the occupation that you earned a majority of the last year's income from or the last occupation that you had for the tax year?

There's no hard and fast rule.

You can enter the one you earned the majority of your income from or you can enter something like:

accountant/janitor -or-

bikini model/nuclear physicist

Or you can try to find a generic term that fits both jobs.

If you were a singer and a dancer, use "entertainer."

If you were a chef and a waiter, use "food service."