This Hindupedia.com page lists various short Mantras and Shlokas that are aimed at solving various kinds of day to day problems we might be facing.
For the given purpose it gives the following Shloka:
For increase in knowledge , to pass in examination (this has to be chanted eight times in the morning)
15.Bhashyathi sarva sashtraani , yechanye niyamaa thadhaa|
Aksharanicha sarvaani thwanthu devu namosthuthe||
I salute her who is the goddess of interpretation of all Sastras , As
well as other works laying down rules as well as all alphabets.
This may be a prayer to Goddess Saraswati although explicitly nothing is mentioned.