Penny had four different jobs during The Big Bang Theory: actress, waitress, bartender, and pharmaceutical sales representative.
When the series begins, Penny is pursuing acting while supporting herself as a waitress at The Cheesecake Factory. Although waitressing is her regular role, she briefly works as a bartender at the same restaurant, notably after returning from an injury. That temporary position is commonly overlooked when counting her jobs.
Penny also has several acting jobs and treats acting as her intended career, even though she struggles to find consistent success. In season seven, she quits at The Cheesecake Factory to pursue acting full-time, but later recognizes that the career is not progressing as hoped.
In season eight, Bernadette helps Penny obtain a position as a pharmaceutical sales representative at her company, Zangen Pharmaceuticals. Penny eventually becomes highly successful in sales and later leads a sales team. Some viewers count only her main occupations—waitress, actress, and pharmaceutical representative—but including her distinct bartending role gives the canonical quiz answer of four.