"En çok hangi kitabı beğendin?"
Translation:Which book did you like the most?
Turkish statements of preference/like/dislike are often expressed in past tense. Even if you are still eating your meal, or trying on an outfit, someone may ask (literally): "Did you like it?" (Beğendin mi? Sevdin mi? Hoşuna mı gitti?)
Present tense (ex. Seni seviyorum; Türkiye'yi severim) tends to be used for on-going/ long-term enjoyment.
There is more info about this here :-)