If you're unsure about the lineage of your Doberman, there are a few physical traits that can indicate whether your dog is American or European. One way to tell is by looking at the shape of the head. American Dobies tend to have a more square-shaped head, while European Dobies have a longer and narrower skull. Another difference is in the ears; American Dobies typically have their ears cropped (or cut) short, while European Dobies usually have natural, un cropped ears. Finally, you can also look at the coat; American Dobermans typically have a shorter and sleeker coat, while European Dobermans often have a thicker and plusher coat.
Of course, these are just generalities and there can be some overlap between the two types - so if you're still not sure which category your Doberman falls into, you can always ask your vet or breeder for help in identifying your dog's specific ancestry.