Dua for exams ( before or during exam):

وَإِن يُرِيدُوا أَن يَخْدَعُوكَ فَإِنَّ حَسْبَكَ اللَّهُ هُوَ الَّذِي أَيَّدَكَ بِنَصْرِهِ وَبِالْمُؤْمِنِين

Wa-in yureedoo an yakhdaAAooka fa-inna hasbaka Allahu huwa allathee ayyadaka binasrihi wabialmu/mineena

“….verily Allah is All-Sufficient for you. He is the One Who has strengthened you and the believers with His help.”

[Surah: 8, Ayah: 62]

Dua after exam:

الَّذِينَ إِذَا أَصَابَتْهُمْ مُصِيبَةٌ قَالُوا إِنَّا لِلَّهِ وَإِنَّا إِلَيْهِ رَاجِعُونَ

Allatheena itha asabat-hum museebatun qaloo inna lillahi wa-inna ilayhi rajiAAoona

“who, when afflicted with calamity, say: “We belong to Allah and to Him we shall return.””  [Surah Baqarah-2, Ayah: 156]