Is there a patron saint for discernment?
The short answer
One possibility is St. Ignatius of Loyola, whose Spiritual Exercises were written to help people discern rightly. Ignatius taught that we should be ready to submit our own judgment to the Church's.
St. Ignatius of Loyola
Ignatius wrote the Spiritual Exercises to aid right discernment. His order, the Society of Jesus, has also been active in higher education and founded a number of universities in the United States.
His counsel
On discernment, Ignatius said we should always be ready to believe that what looks white to us is black, if the hierarchy of the Church defines it so — so as never to go astray.