What should I do with a gold chain I found in a market, and should I sell it and donate its value, or donate it as is, knowing that I consider it of little value?

The trivial lost item that its owner does not inquire about means that the finder of a small lost item may benefit from it, and is not obligated to announce it. This has been narrated from Omar, Ali, Ibn Omar, and Aisha. As for the necklace, it is valuable and must be announced for a full year in places where its owner might find it. If a year passes and its owner is not found, you are permitted to benefit from it while guaranteeing it, or to give it as charity, or to sell it and give its price as charity on behalf of its owner. If its owner comes one day, he is given the choice between affirming the charity or receiving its value.