I lent a friend 6000 yuan, without any IOUs or witnesses. I don't know how to ask.

This is relatively simple. The first method is that you call him, record, describe the client, the process and amount of borrowing money, and he just needs to admit it. The second way is for you to coax him into writing you an iou. The third method is to send short messages. You text him and ask him when he will return your 10000. He will definitely send a text message saying that he borrowed 6000 yuan instead of 10000 yuan, and the text message is on your mobile phone, so that evidence can be obtained. After obtaining the evidence, a public prosecution was initiated in accordance with the Civil Procedure Law of People's Republic of China (PRC), General Principles of Civil Law and Contract Law.