I have problem in understanding where the selected artikel will dispayed.

For example, I'm on my Master Site and select a Multisite in the parameter panel perhaps it is the <Master Site>, at the menu type "Multi Sites Category Blog Layout".

Where will it dispayed? On the Mastersite only? On all Sites? On the selected Site? Is there a posibility of vise versa so that I can handle it from a Slave Site?

The "Article Sharing for JMS" works like the standard Joomla "Article" menu.
When you create a menu that select the menu type "Article", you display in your current website the article(s) using a "category as a blog", "category as a list", "section as a blog", "section as a liste".

With the "Article Sharing for JMS" you are doing exactly the same.
The only difference is that you can select FROM which website you read the article that you display in your current website.
You have an additional parameter to select the "Site" where you read the articles.
The site correspond to the list of slave site that are defined in you JMS Multisites and that you can see from the "manage site".
You have an additional one that is the "<master DB>" that does not appear in the list of site as this is not a slave site.

So when you create a menu item, you select from which website you are reading the articles and after the other parameters are identical to the standard Joomla article menu item.

So, when I get it right there is no way to share articles from the Mastersite? In other words, I have a Master Site to operate from and another one to share from?
I would like to do it all over the Master Site.

But I also tried to share a article between one slave to another but all I get was a blanc page?

Only sharing from Slave Site to Master Site works. Is this the way?