Hi
I the Notifikation Modul I miss the little log out button. ?

Hi,

at top right for the notification module, there is no logout button. this is by design.
but the logout button exist at jomsocial toolbar.

because you are using JA social template. that template having this CSS:
/templates/ja_social_ii/local/css/themes/violet/extras/com_community.css line 15

html .joms-js--logout {
  display: none;
}