Hello
Where canI see that my google sitemap works correct,
before I submit it to google?

Well two things.

First, I edited your title, no worries, just because your problem is not exactly how you first think it was and will be useful to others.

In your case phpBB is installed in a sud-domain and the Google sitemaps system only allow URL to be listed if they are not only within the same domain (or sub-domain) but as well within the same folder as the SitemapIndex (cannot list www.example.com/example.html from within www.example.com/folder/sitemap.php).

Then, you should thus install mx Google Sitemaps phpBB side, not mxBB.

So far your Google sitemapIndex is here : -http://www.detektoreninfo.de/sitemap.php

And it appears you'll need as well to implement the rewriterules located in the contrib/ .htaccess.

Good point you made it to upload the correct premodded file for the phpBB SEO mixed mod rewrite

So basically, you just need to uninstall the mx Google Sitemap module from mxBB (ACP uninstall) and then install it in phpBB. Your sitemapindex will be located in : -http://www.forum.detektoreninfo.de/sitemap.php (will be sitemaps.xml with mod rewrite )

You should just redo as before for the premodded file and add the contrib/ folder's .htaccess rewriterules in your forum's .htaccess.

To make sure it works, just load the sitemapIndex and manually follow links to see if they work and provide the correct URLs. You just need to test one forum sitemap and the forums sitemap (sitemap-forum.xml or sitemap.php?forum and on of the others)

Once checked, just submit

Think I forgot to load sidemap.php to forum folder...
I take a look on xml urls and think they works

So I must submit 2 sitemap urls to google?
Because ther are 2 domains (subdomain)?

Your problem here is you cannot list URL not being part of the same domain (or sub-domain) as the sitemapIndex.

Google will refuse any occurrence of -http://www.forum.detektoreninfo.de/ in -http://www.detektoreninfo.de/sitemap.php

The only interest to keep mx Google sitemap installed in mxBB portal would be to list it's pages URLs (eventually the mx_kb one as well), but no forum URLs.

But you'd really need the module installed twice.

And to delete modules/mx_ggsitmaps/includes/index_forum.php and /mx_ggsitmaps/includes/sitemap_forum.php but to leave the other ones and to only use those two in forum/mx_ggsitemaps/includes/

Besides, the forum URLs your sitemaps provides are the good ones

++

I delete the index_forum.php and sitemap_forum.php
Now the Portal sitemap.php link only to forum.domain.de/mx-sitemap.xml ?

which is what you want, because phpBB URL must be listed under it's domain (because of Google rules).

Actually, you could then just submit directly -http://www.forum.detektoreninfo.de/mx-sitemap.xml for your portal and -http://www.forum.detektoreninfo.de/sitemaps.xml for you forum.

But submitting the sitemapIndex for mxbb portal won't bother Google and will allow you to add further listing in the future, so I advise you to submit -http://www.forum.detektoreninfo.de/sitemaps.xml as is for the portal.

++