Do i miss something, if I open the quest window, i don't see any indication of how many of my grouped friends have the same Quest.

In the original it would for example say [1] Indicating that one more Member has the same quest.

Do I miss something, or is this not implemented?

 Okay, i found it.

 I not came to the idea to look after the Quest Title, but there it says (1 Name) 

 However with some Quests the Text is not visible ,because the Text is too long.

 Or do i miss more? Maybe an option to set it like it's on the Default Quest log?

 I have also noticed this visibility issue. I was grouped doing the Horseman quest and wanted to see who in the group had a summon. So I looked in the quest log and the party members that had the quest was cut off. I could not see the actual amount no matter how far wide I stretched the quest frame.

 Okay, a quick update, incase someone else has the same Issue.

 I noticed you can enlarge the "Rows" by clicking on the small bar at the top, so it's possible to make the display of the Quest-Title (incl. the Amount of other Players who share the Quest) bigger, therefore it's kinda fine like that.

 Even it's a bit harder to read like that ,then in the standard-wow interface.

 Idea: why not just color the quests you share with others, in a different color or have a different background ,to highlight those, once you are groupped. That would help alot.

We are in the process of adding a quest sharing interface that will allow you to easily see the quest status of all party members.  We hope to get this in a version very soon.