Complex sentence: Prior to that, Slavnov competed with Julia Karbovskaya, with whom he won the silver medal at the 2002 World Junior Figure Skating Championships.
Split into simpler sentences: Prior to that, Slavnov competed with Julia Karbovskaya, with whom he is the 2002 World Junior silver medalist. Slavnov originally skated with Julia Karbovskaya and won silver at the 2002 World Junior Figure Skating Championships.