It is said that this happens in close proximity. So it is always referenced together. What happens when you get the knowledge and how do to transition to the Fruit? What happens just before the knowledge of the path?
There are some suttas which give an indication that there is a time gap between path and fruit meaning that the fruit does not happen automatically following the path.
Udana 5.5 - Uposatha Sutta: mentions "stream-winners & those practicing to realize the fruit of stream-entry; once-returners & those practicing to realize the fruit of once-returning; non-returners & those practicing to realize the fruit of non-returning; arahants & those practicing for arahantship."
SN XXV.1 - Cakkhu Sutta: describes the saddhanusari and dhammanusari - disciples by faith and wisdom respectively. Both are described as following the path - "one who has entered the orderliness of rightness, entered the plane of people of integrity, transcended the plane of the run-of-the-mill", and that "He is incapable of passing away until he has realized the fruit of stream-entry". It clearly implies a time gap between path and fruit.
AN 4.170 - Yuganaddha Sutta: says that "developing tranquility and insight the path is born. He follows, develops and pursues that path, and by doing so his fetters are abandoned." Again there is a time gap implied.
Knowledge of the path is simply the first realization of Nibbana as one of the particular kinds of Aryas. In other words, the first time a person experiences Nibbana as a Sotapanna, Sakadagamin, Anagamin, or an Arahat is called knowledge of the path. During the path-knowlege, the fetters are destroyed or greatly weakened . Knowledge of the fruit is the same except that it doesn't cut away at the fetters in the same way so it is classified differently.
Knowledge of the fruit occurs automatically after knowledge of the path. You don't have to do anything specifically to make it happen.
Here is a description of these knowledges from the Visuddhimagga:
Here is a simile for this. An archer, it seems, had a target 3 set up at a distance of eight usabhas (about 100 yards), and wrapping his face in a cloth and arming himself with an arrow, he stood on a wheel contrivance (a revolving platform). Another man turned the wheel contrivance, and when the target was opposite the archer, he gave him a sign with a stick. Without pausing after the sign the archer shot the arrow and hit the target. Herein, change-of-lineage knowledge is like the sign with the stick. Path knowledge is like the archer. Path knowledge’s  making Nibbána its object without pausing after the sign given by change-of-lineage, and its piercing and exploding the mass of greed, hate and delusion never pierced and exploded before, is like the archer’s hitting the target without pausing after the sign.
And not only does it cause the piercing of this mass of greed, etc., but it also dries up the ocean of suffering of the round in the beginningless round of rebirths. It closes all doors to the states of loss. It provides actual experience of the seven noble treasures. 4 It abandons the eightfold wrong path. It allays all enmity and fear. 5 It leads to the state of the Fully Enlightened One’s breast-born son (see S II 221). And it leads to the acquisition of many hundred other blessings. So it is the knowledge associated with the path of stream-entry, the provider of many hundred blessings, that is called knowledge of the path of stream-entry. The first kind of knowledge is ended.
Immediately next to that knowledge, however, there arise either two or three fruition consciousnesses, which are its result. For it is owing to this very fact that supramundane profitable [consciousness] results immediately that it is said, “And which he called the concentration with immediate result” (Sn 226), and “Sluggishly he reaches what has immediate result for the destruction of the cankers” (A II 149), and so on.
(Visuddhimagga Chapter XXII 12-15, http://www.accesstoinsight.org/lib/authors/nanamoli/PathofPurification2011.pdf )