Well there's no perfect player, since it's dependent on tactics used and who you're playing against, but generally speaking (very generally) a C will be less a part of your offense than your PF, even playing an inside focused offense, so naturally, ID and RB are important. I'd still say IS should be trained because they do still shoot. SB is heavily debated about it's usefulness. I'd say up to Respectable is fine. More than that can be debated endlessly. Passing is somewhat useful for dishing it out to an open shooter, though obviously it shouldn't be as high as a guard. And don't neglect your Stamina.
As for PF, all those skills mentioned for C, but he'll also need Driving and Jump Shot. Handling helps as well, but again, probably not as high as a guard.