Answer
"Sergei Pavlovich Diaghilev" is pronounced as “sir-GAY pahv-LAH-vich dyah-GIH-lev”. The stress is on the first syllables of "Sergei" and "Pavlovich". The "-ev" at the end of "Sergei" should be pronounced like "eff". As for "Diaghilev," remember that "Di-" sounds like “dee” and “-ev” sounds like “eff”.