Answered by: Maulana Abrarul H. Hasib
Assalamwalaikum, which is more beneficial. Praying 2 nafl for something to happen ( good score on an exam) or to read Quran ( specifically Yasin)
In the name of Allah, the Most Gracious, the Most Merciful
Reciting Qur’an and performing Salah has its own virtues and fadheelah. Both are means of rewards and blessings. Both can have preferences over the other due to different occasions, times, and objectives.
Performing Salah will be recommended on this occasion as Salah consists of multiple ibadat such as Ruku, Sajdah, Recitation of Qur’an, and submission to Allah Ta’ala.
It was narrated that Thawban said: “The Messenger of Allah said: ‘Know that the best of your deeds is Salat (prayer).'” 
You may also recite Surah Yaseen if you wish to. Rasul Sallallahu Alaihi Wasallam said: “Whoever recites Surah Yaseen at the beginning of the morning, his/her necessities will be fulfilled.”
You may also recite following Dua:
رَبِّ اشْرَحْ لِي صَدْرِي وَيَسِّرْ لِي أَمْرِي وَاحْلُلْ عُقْدَةً مِنْ لِسَانِي يَفْقَهُوا قَوْلِي
Transliteration: Rabbish rahli sadri wa yassirli amri wah lul uqdatan min lisaani, yaf kahu kauli. 
And send peace and salutation upon the Messenger of Allah Sallallahu Alaihi Wasallam abundantly.
May Allah Ta’ala make all the exams easy and may you be successful in the exam.
For more information visit the link below
Only Allah knows best
Written by Maulana Abrarul H. Hasib
Checked and approved by Mufti Mohammed Tosir Miah
Darul Ifta Birmingham
 Sunan Al-Darmi 3461.
 Surah Taha, V. 25-28
 Sunan Ibn Majah 277, Pg. 87, Darul Fikr.