Q: Is it recommended for the Imam to make dua after prayer? If so, how should it be done and should the people behind him say Amin?
A: It is recommended for the Imam to turn to the congregation and make dua after the obligatory prayers especially Fajr and Asr due to the presence of the angels. The followers should respond to his dua by saying Amin.
From the manners of dua at this time is to raise the hands to chest height with open palms facing upward, to begin by praising Allah and end by sending prayers of peace upon the Prophet, to beseech Allah with His beautiful names and lofty attributes, and to supplicate using a comprehensive and reported dua.
Source: Sharh al-Muntaha