It doesn’t if it’s not on the label somewhere. In the US it has to say if it contains any significant amount of caffeine. It won’t be on the ingredients list if one of the ingredients is where the caffeine comes from though (e.g. coffee or chocolate). But it’ll still say underneath that or elsewhere “Contains __g of caffeine.”
Umm is it not just carbonated water , and flavourings i.e fruit or whatever flavour it is .
If caffeine is not on the list then , its got no caffeine unless they have managed to hide it to get people hooked