A swipe file is copy industry jargon for 'headlines that work.' Copywriters and marketers tend to assemble a swipe file over the course of a career, and you'll see these same headlines over and over. For example, 'New Year, New You' is a common headline that marketers will use around the turn of the year in a variety of industries. The interviewer wants to know if you've been creating a swipe file over the course of your career.