A letter from the post-2015 co-facilitators containing the themes for the six interactive dialogues to be held during the post-2015 Summit has been posted at: https://sustainabledevelopment.un.org/post2015.
The modalities for how these six interactive dialogues will be organized are outlined in General Assembly resolution 69/244 (annex II): http://www.un.org/ga/search/view_doc.asp?symbol=A/69/L.43&Lang=E