It is permissible to eat if the doubt is whether it has been extracted from an animal or vegetable. But, if it is known that it was derived from an animal, then it is not permissible to eat without ascertaining that the animal was slaughtered according to Sharí‘a. This prohibition applies, as a matter of obligatory precaution, even if it was extracted from animal bones.
Of course, if a chemical change occurs (Istihala) in the original ingredients during the process of manufacturing the gelatin, there is no problem at all in eating it.