Firstly, "How do you, politely, ask someone to return the book or money they borrowed from you?" Secondly, there are several different ways to do this. 1. You can try to funny approach. Try to say it jokingly if possible. If they mention lending something to someone or if they mention borrowing something from someone you can say some like (smile while you say it) "Don't you still have my ___ book?" or "Says the girl who still owes me 200 Yuan." maybe a slight chuckle with a smile. Just make sure you are being friendly about it. 2. The serious approach is to let them know you aren't angry but that you really need it back. If it is a large sum of money perhaps offer a payment plan. Small amounts paid back each month. Let them know you know they are having a financial problem, you want to help them, but you need to be paid back or they need to show they have good intentions to do so. Again, let them know you are their friend. 3. The nonchalant approach is to just mention it in passing. "Hey. Don't you still have my Harry Potter book? Do you think you could bring that with you the next time we meet up?" 4. Sneaky "I can't find my Harry Potter book. I have no idea what I did with it." There are many ways to do it but your best bet is to always show you are not angry.

یک سوال خوب است می توانید اینجور بپرسید: "If I could have that money/book I lent you back?" جواب آن فرد ثینی درست نیست :D اگر می خواهید بسیار دلیل گفتی، لتفن این گفتید: "I need it back to ...... (return to the library) (buy my lunch) (read it my self)" انگلیسی شما خیلی خوب است!!

For book, I will say" I have other friend who wants to read this book too, so can you return my book, I am so sorry to bother you to do that". For money, I will say" my dear friend, I need some money to pay for my daily use, but now my money is not enough,so can you return me some of your money if you have, thank you for you deed."

You could say.. "Can you please return my book?" or "Can you please return my money?"