I says on the ATP website. But I just chacked, and Fed has 13 (Doha, AO, Dubai, Davic Cup, RG, SW19, OGs, Rotterdam, Halle, IW, Miami, Madrid and Rome) and Novak has 11 (AO, RG, SW19, IW, Miami, MC, Madrid, Rome, Toronto, OGs and Dubai). Even not counting Feds Davis Cup, he still played 1 more tournament than Novak. And then some Fed fans say Novak is vulturing but the weakest tournament he played was the strongest 500 of the season.
Weakest tourney he played is Toronto.