Larian Studios Forums Divinity - Original Sin Divinity - Original Sin - General Does Attitude only affect the character talking?

Or the whole party? I ask because if it's only for the character talking, then skills like Stench or Know-It-All on your companions seems completely viable, possibly even awesome?

That is correct.
Anything you add to a character only affects that character, unless specifically noted such as Leadership affecting everyone ELSE in the party that can see the character.

Thus, if you increase Perception on a character, THAT needs to be the character you walk around with while the others follow. If you add Charisma and/or Politician to a character, THAT needs to be the character doing the talking with NPCs.