What do Keu Mone Mone(Bengali) and Daiya Daiya(Hindi) mean ?

I don't speak Bengali but I can help you with the Hindi part. Daiya doesn't mean diamond. "Daiya" is just a poetic term which means almost nothing. It is an expression to say something like "Hey". In this song, Daiya is used so that it can rhyme with the tune. Many Bollywood songs have this kind of cute words that don't have real meanings, instead are used to make it catchy.