Hi Zamara, I just received an email from Eric askin me to see if I might be able to help. However, I have never used a Geman keyboard, since I live here in the US, now.
Eric, I am not sure what the ASCII code for this key combination is. If the key shown on the image in your post doesn't work, may be Zamara could use the <alt> keypad combination, such as <alt>0252 for ü, or <alt>0246 for ö, and the like.