What is our duty toward an uncle who has been missing for 28 years in the Iraq-Iran War, his fate still unknown? Should we supplicate for him or ask for mercy upon him?

Your uncle's case is treated like that of a missing person until authentic news of him arrives or he dies. You must search for him by all available means, and supplicate frequently for his relief if he is a captive, and for mercy and forgiveness if he is deceased or alive. It is good to give charity on his behalf and to repay his debts if possible.