when should we recite ayyat-ul-kursi after the salat in the du'a, I mean we should read it after the fardh or after the sunnate?

Upon the completion of Fardh Salaat, two situations could come about:

1. Either there are Sunnah Salaats to be performed after the Fardh Salaats, e.g. Fajr, Asr, etc.

2. Or there are no Sunnah Salaats to to be performed after the Fardh Salaat, e.g. Dhuhr, Maghrib, Esha.

Therefore, those Salaats after which there are no Sunnats, the Dhikrs should be read immediately. And those Salaats after which there are Sunnats, the Sunnat Salaats should be completed and then the Dhikrs should be read. To delay the Sunnah Salaats for longer than the duration it takes to read ‘Allaahumma antas salaam wa minkas salaam, tabaarakta yaa dhal jalaal wal ikraam’ will be Makrooh. (Haashiya Tahtawi vol.1 pg.312)

and Allah Ta'ala Knows Best

Mufti Ebrahim Desai