You'd have to develop a replacement of the OssnSmilies component
which would need to evaluate the position of the clicked 'opener' icon on screens larger than w X h pixels (your choice) and open the selector box a little bit below. Perhaps all that can be delegated to bootstrap tooltips ... see
https://codepen.io/team/bootstrap/pen/zYBXGwX?editors=1010

This is still not nice - on my big PC monitor I've to go over the complete display to get to the emojis

how can I change it?

Sorry if my answer was confusing - I was just referring to the English version ... (Posten = Post)

Anyway, wherever (inside of a post, a comment, etc.) you open the emoji selector box, it will always be placed bottom right. It's designed like that to prevent overlapping.

No..

I clicked the emoji icon below the „Posten“ on the top of the page and not below the post and the emoji box opened on the bottom but it should open under the field I clicked the emoji.

ok,
you clicked the emoji icon below the post
and a box opened bottom right to let you choose an emoji to be inserted into your text at the current cursor position
(that's the default way)
so ... what's the problem?

The first image was an iCloud image too and that worked, but here:

https://ibb.co/fSdX2X0

Please share a direct image URL we can not able to see icloud images in editor.

When I click on the emoji panel OSSNWall posting on the top of the page, the emoji panel is opening on the bottom of the page

Do you mean they are outside of the view?