The Jedi Knight is a very important class for the Jedi Order. In the Old Jedi Order, the Jedi Knights were the defenders of peace and justice in the Galaxy. After the Great Jedi Purge, the role of Jedi Knights would take on a much different meaning.
Under Luke Skywalker, the New Jedi Order's primary goals are to follow the will and guidance of the Force, grow and expand the Jedi Order, and defend the Galaxy from the threat of a re-emerged Sith Order.
There are no strict guidelines as to how and when a Padawan is brought into Knighthood, due to the small size of the New Jedi Order. The decision is made by the leading Jedi Grand Master, Luke Skywalker, and is enacted through a ceremony meant to honor the Padawan and respectfully declare Knighthood on the student.