Favourite 2020 POPSUGAR Reading Challenge Prompt: Book on a Subject You Know Nothing About Readers expanded their horizons with each 2020 POPSUGAR Reading challenge prompt, but "book on a subject you know nothing about" won out as the fan favourite this year. POPSUGAR Book Club member Kelly Bloom Barbieri said this one "encouraged me to take on a period and history of a country that I knew very little about."