Hi Hingoa,
Welcome to Apple Support Communities. We understand that you were gifted an iPad, purchased in the US, but are hoping to return it to an Apple Store in Germany. We'd like to help.
From what we see here, the iPad would need to be returned/replaced at a location within the same country that it was purchased: Returns & Refunds
Exchange of an item
* Items purchased from an Apple Store can be exchanged at any Apple Store in the same country.
* Items ordered from the Apple Online Store that arrive damaged or faulty can be returned to any Apple Store in the same country.
If you have additional questions about this, it would be best to contact Apple Support. You can get that conversation started here: Contact - Official Apple Support
Hope that helps.
Cheers!