Looks to have a steel bar balance weight in the small radius leading edge which also appears to be flat bottomed  so suggestive of a frise type control surface normally used on ailerons. They used several visually different styles of control surface balance weights on the Dornier and other German aircraft which should help to narrow it down. if it’s 217 I think likely  outer most part of aileron as other control surfaces appear to be balanced externally.  Bill Gunstons aircraft cutaway book will help but captions cannot be always trusted to be correct.