Unless it specifically mentions on the packaging that something contains nuts, it isn't supposed to, at least in the EU.
That doesn't mean there can't be traces of something in it left over from a previous production batch, and many products will warn for that in the case of nuts, but that's it.
That's nothing specific to chocolate btw, the same is true for pretty much all food stuff sold packaged in the EU, it MUST have a list of ingredients.
But if you seriously need to avoid an allergen, best shop only in specialty stores where they know the product better than would a supermarket clerk or someone manning say a gas station.