.gr domain will only ever rank on Google for searchers from Greece. There is no way to target a
.gr domain to worldwide users of Google. See I'm using a vanity country code top level domain (ccTLD), can I persuade Google to geotarget a different region?. It doesn't make sense to put your English content on a
.gr domain name unless it is focused just for English speakers in Greece.
I don't think there are many Greek speakers outside Greece, so it is OK to have your Greek content on that domain. In fact, it will probably enjoy a ranking boost on the
.gr domain compared to on the
.com for searchers from within Greece.
When you publish the same content on two different domains (or any two different URLs), Google does see it as duplicate content. Google doesn't usually penalize for duplicate content, Google usually just picks one of the two to index. See What is duplicate content and how can I avoid being penalized for it on my site? Rather than let Google choose, you usually want to choose yourself. It is usually best to host the content in just one place and redirect the other to it.
I would recommend putting your Greek content on the
.gr domain and putting your English content on the
.com domain. That way:
- The content will be on unique URLs and avoid any duplicate content issues.
- Your Greek users will have a local and comfortable
.gr domain name which should rank better within Greece.
- You will be able to target your English content worldwide which you can't do on your