The knowledge in question is not a quantity of information and is not a belief that has been justified. It is viveka, discrimination: the sustained ability to tell what is permanent from what is not, and to stop treating the impermanent part as oneself. A person can accept the doctrine completely and have no jnana at all, which is why the tradition treats the path as difficult rather than merely intellectual.
Vedanta sets out four qualifications a student is expected to bring before beginning, and they are demanding. The first is that discrimination between the eternal and the transient. The second is dispassion, vairagya, an absence of appetite for the results of action here or hereafter. The third is a group of six, comprising calm of mind, restraint of the senses, withdrawal from what distracts, endurance, faith in the teaching and the teacher, and one-pointed settled attention. The fourth is mumukshutva, an urgent desire for liberation strong enough to outweigh everything else.
The list is not a bureaucratic hurdle. Its function is to explain why the path is described as direct and demanding at once: the discrimination itself is simple to state, and holding it steadily against a lifetime of habit is not something an unprepared mind can do. That is also why the tradition places the other paths alongside it rather than beneath it, as ways of acquiring exactly these qualifications.