"I work as a doctor."
Translation:Pracuję jako lekarka.
I cannot think of a situation where you would use Accusative after 'pracować'...
"pracować jako" is a fixed construction that means "to work as", and it is one of the rare cases when you use Nominative for something else than the subject of the sentence.
"Pracuję jako lekarka" works, but it is not masculine animate. It is feminine (and animate, but it doesn't matter for feminine). "lekarz"/"lekarka" is among those professions where a woman can use either a masculine or a feminine version of the profession's name.