The following code will display the name of the first bookmark in the selected text and if there is none in the selected text, it will display the name of the first bookmark in the document after the start of the selected text if there is one. Otherwise it will display a message advising that there are no bookmarks in the document after the start of the selected text:
Dim rng As Range
Set rng = Selection.Range
If rng.Bookmarks.count > 0 Then
MsgBox rng.Bookmarks(1).Name
Else
rng.End = ActiveDocument.Range.End
If rng.Bookmarks.count > 0 Then
MsgBox rng.Bookmarks(1).Name
Else
MsgBox "There are no bookmarks in the document after the start of the selected text."
End If
End If