V0idhead: If you hover over the 3 mental stats on the character page to the right of the portrait the popup will say something like "Alchemist, Magus, etc. gains bonus spells based on intelligence".
But if you have an archetype that overrides this you will have to look at the class-chart these have an icon on level one that describe to which stat it was changed, albeit somewhat vaguely. For instance for Empyreal Sorcerer, it's the angel-looking icon and the popup says "Empyreal Sorcerers derive their powers from insight rather than their personality."
You're probably better off with the chart, but you can get the info during the game.
I noticed this too that basic classes are descripted in Int/Wis/Cha info. But anger got better of me when I couldn't find anywhere Woljif's usage of Int
