Google Groups – Mark a Topic as Unread

It isn't possible to do this whilst browsing Google Groups via the web.

It is possible to do this if you subscribe to the groups via Google Reader.

Now, the reply you posted is under review due to the particular Google Group's Settings. Now, you cannot know when it gets accepted (in the same way as we - users with less reputation try to edit a post in SE and get the "until it is peer-reviewed" message. When the edit is accepted, we do not receive any email-notifications nor any inbox message in SE. All we can do is check if our reputation in the particular SE site has incresed and if it has, see the reason behind it).

All you can do is go back to the Group once in a while and manually check if what you posted is accepted.

You cannot see the queue of pending post as you are not a moderator or admin of the group (or whatever they call), in the same way as we cannot see the list of question and answer edits waiting to get approved in SE - only members with very high reputation can do it.