I want to know regarding the duas after fard salat. eg. at zohar we pray 4 sunnat, 4 fard, 2 sunnat and 2 nafl. Now should I pray the duas after the 4 fard salat or after completing the whole salat?

To answer your first question there is no stipulation in the Shari'ah on the Du'aa after Fardh Salaat.

To make Du'a in any form (loudly, softly, collectively, etc.) and any time (before, after Fardh Salaat, etc.) is permissible. While there are substantiations for the different forms and times of making Du'a, Shari'ah does not restrict the making of Du'a in those forms or times not specifically substantiated in Shari'ah. At most, making Du'a is permissible and an act of great virtue and merit. It is not permissible to project a permissible act as compulsory as this is projecting a wrong view of the Shari'ah, thus, causing distortion of Deen.

To regard the collective Du'a after Fardh Salaat or Sunnah Salaat as compulsory will be Bid'ah as that projects the incorrect image of Shari'ah.

Loud Du'aa after Salaat is established and proven by many Ahaadith. It is narrated that Rasulullah (Sallallaahu Alayhi Wasallam) should say after Fajr Salaat, 'O Allah, I ask you for beneficial knowledge, accepted actions and pure sustenance.'

In another Hadith, Rasulullah (Sallallaahu Alayhi Wasallam) told Mu'aadh ibn Jabal (Radhiallaahu Anhu), 'I love you, so say after every Salaat, 'O Allah assist me in your rememberance and gratefulness.' (Fataawa Mahmoodiyah vol.10 pg.238)

You, however, can practice certain Masnoon acts after the Fardh Salaat like the reciting of Tasbeeh, i.e. 33 times Alhamdulillah, 33 Subhaanallah and 34 Allaahu Akbar. Also, you can recite Aayaatul Kursi, when you complete all your Sunnah and Nawaafil you may then make your Du'aa.

and Allah Ta'ala Knows Best

Mufti Ebrahim Desai