Translation:What year was last year?
This is one of those instances where it helps a lot to know the kanji! If you can think of them in terms of how they look (and what they mean) instead of how they sound, it's harder to mess them up.
kyou = 今日 = today ("this day")
kyo = 去 = past (so, 去年, "past year," last year)
Useful phrase when you either don't know what year it is... or don't know how to deduct one...
actually 去年 should be pronounced きょねん. if the voice pronounced it as とし, it's a mistake on Duo's part.
とし is the kun'yomi for 年, meaning that it is the reading 年 takes when it's read on its own, without being conjoined to any other kanji. But because it's joined with 去 here, it takes the on'yomi, ねん, instead.