Can Nafl prayer be offered or not after Jama'at has been established?

 Q 5: Can Nafl prayer be offered or not after Jama'at has been established?                                                                                                                                                                  

Answer: No Nafl prayer even Sunnat-e-Muakkadah can be offered after Jama'at has been established except the Sunnat of Fajr and that too when one is sure to join Jama'at even Qa'adah after completing Sunnat otherwise not. 

These Sunnat should neither be offered adjacent to the row of Jama'at nor behind the row but at such a place in mosque that there is a cover between him and the Jama'at. 

And in case one finds Imaam (Jama'at) in Rukoo and he does not know whether it is the first Rakaat'sRukoo or of the second then he should abandon Sunnat and join Jama'at.