Is it justifiable that the Indians want the Koh-i-noor or the Greeks demand the return of the Elgin Marbles from Great Britain? How would you respond to this?

I think they’re entirely reasonable desires grounded in nationalist sentiment following a long legacy of colonialism: Queen Victoria took the Koh-i-Noor diamond as part of the Treaty of Lahore, just as a few clauses above the British had taken the Punjab from the Sikh Empire; similarly, the Elgin Marbles were taken by the Earl of Elgin by getting a decree from Istanbul, only a few years before the Greeks would rebel against Instanbul, eventually overthrowing them.