Hello i Run zenphoto now abaout 2years, and ist Works Geraet.
Now i want to add one more domain, the galery should bei usable from both of my Domains, how can i add id?

You have to add additional domains via web server and point them to the same location. Zenphoto is not involved in that. Ask your webhost about that.

However, it is not recommend for SEO reasons to have a site be accessible on two separate domains. Instead redirect additional domains to one domain you consider the main domain. Search the web for the term "duplicate content". Ask your webhost about such redirections, too.