Caffeine does not occur naturally in any of the ingredients of any soda (at least the well known ones). It was added to the soda, originally for medicinal purposes, and now probably because people demand/need/are used to it. Any soda marked caffeinne free do not have any caffeine, also typically orange (or other fuit flavored) soda, most root beers, sprite, 7-up do not contain caffeine.
Also, if cafeine does not show up on the ingredients list then it doesn't contain any.
The reason decaffeinated tea and coffee still have caffeine is because it occurs naturally in the bean or leaf, respectively, and has to be stripped out. But it can't be completely removed without removing things like taste or aroma. The stripping process is actually quite interesting.