Kettler is one of those brands that occupies an interesting corner of the eMTB market. They're a German company with a long history in fitness equipment and recreational bikes, but for frame manufacturing they follow the same pattern as the vast majority of the industry: frames are welded in Asia, primarily Taiwan or China, then finished and assembled in Europe.
Specifically, Kettler has used manufacturers in Taiwan for their aluminium frames. This is the same supply chain that serves most mid-range European bike brands. The welding and heat treatment happen at the factory, then frames are typically shipped to Europe for painting, decaling, and final assembly. Some of their higher-end models have historically been finished at their facilities in Germany, though Kettler's corporate history has been bumpy (they went through insolvency in 2019 and were restructured).
For the Scarpia specifically, I don't have a confirmed factory name in my records. If this matters for warranty or quality reasons, your best bet would be contacting Kettler directly or checking the frame serial number, which sometimes encodes the manufacturer. Worth noting that Asian-welded frames are not inherently inferior; some of the best framebuilders in the world operate out of Taiwan, and the quality control at places like Kinesis or Giant's Taichung facility is genuinely excellent.