Bismillahir Rahmanir Rahmeem
As exams kick off this week around the UK, we often get asked for Du’as to help and ease exam pressure. Here is one I have personally read and found beneficial:
اللّهُـمَّ لا سَهْلَ إِلاّ ما جَعَلـتَهُ سَهْلاً وَأَنْتَ تَجْعَلُ الْحَزَنَ إِذا شِئْتَ سَهْلاً
O Allah, there is no ease except in that which you have made easy and you make the difficult, if You wish, easy. 
P.S. One should read with conviction and certainty. Also, offer two Rak’ah Salatul Hajah before the exam. It can be the night before or day before, not necessarily the morning of the exam.
Ismail Ibn Nazir Satia (One who is in dire need of Allah’s forgiveness, mercy and pleasure)
12 Shaban 1437
 Sahih Ibn Ḥibbān (974);
‘Amal al-Yawm Wal-Laylah (351).