The Rambam held that the 13 Articles of Faith needed to be accepted because of proofs. Not "believed", not accepted because you were taught them by an authority figure or read them in a book. But each person should be able to prove them for themselves. (Igeres Taiman)
R Chaim Heller noted in his translation of Sefer haMitzvos (1914) that the Rambam uses the Judeo-Arabic word "itakad", which means "knowledge". R Yosef el-Qafih, commonly known as Rav Kapach (of the Yemenite community) has a similar footnote in his translation (1994).
One could ascribe to the element of the Rambam's position that emunah is knowledge without agreeing to the facet of his position that you asked about -- that knowledge is most centrally something you can prove. At least, not in the sense of a philosophical proof.
Perhaps the most famous line in Epistemology is Plato's definition of "knowledge" as "a justified true belief." (That definition is flawed, most famously by the Gettier Problem, but it's still the basis of all such discussion.) There are other ways to justify belief than Philosophical Proof.
Before the Rambam, Rav Yehudah haLevi (Kuzari sec. 1) even belittles the entire concept of philosophically proving this kind of thing. In his dialog, he has the Rabbi say (1:13):
That which you describe is religion based on speculation and system, the research of thought, but open to many doubts. Now ask the philosophers, and thou will find that they do not agree on one set of actions or one principle, since some doctrines can be established by arguments, which are only partially satisfactory, and still much less capable of being proved.
And later in that section (1:63), he pardons the Greek philosophers for their errors in that they lacked a tradition and had to rely on a second-best -- philosophical deduction:
There is an excuse for the Philosophers. Being Grecians, science and religion did not come to them as inheritances. They belong to the descendants of Japheth, who inhabited the north, whilst that knowledge coming from Adam, and supported by the divine influence, is only to be found among the progeny of Shem, who represented the successors of Noah and constituted, as it were, his essence. This knowledge has always been connected with this essence, and will always remain so...
Skipping out of our tradition and ahead to Modern Philosophy...
This skepticism about the perfection of proof becomes fundamental to the Empiricists, who believed that only experience of the outside world can produce reliable knowledge. And then it really came to the fore with Immanuel Kant, who denied our ability to experience what's really "out there" altogether. That because everything we experience and think are shaped by pre-existing human categories, the way people work, none of it is real and objective. We only know the world of phenomena, how things look to humans, and only can reason with those more limited givens.
And this progresses through the Existentialists and the Post-Moderns. So that today, in most College Liberal Arts departments, there is no concept of objective truth altogether. Never mind being able to prove things.
I think the Kuzari's argument would be classified today as a kind of Reliabilism. We trust our Tradition because it comes from sources that have proved themselves reliable in the past. Which is a way to justify belief, so -- contrary to the Rambam -- today's philosophers would consider trusting a fact because you were taught it bey someone you trust would be considered knowledge.
Another possible justification could be first-hand experience. And I think this happens far more often today. Someone experiences their first Shabbos. It agrees with them, provides meaning to their lives. I don't just mean the aesthetics, that they enjoyed themselves, but the experience itself -- the thing they enjoyed. Like the way mathematicians are likely to agree on what makes a proof "beautiful" or "elegant", there is an objective feature they are identifying and giving an aethetic judgement about. That math proof, or living that Shabbos, has the features one expects of truth.
Or, when you learn something about the laws of property that somehow has implications in the laws of Shabbos and resolve what seemed to have been an unrelated question. Truth works like that, not invented systems. If this happens to someone when learning Torah often enough, they stop wondering whether or not they can prove the Torah is from Hashem. Or whether halakhah as we now practice it, which is largely a product of a system, is a product of the system Hashem gave us at Sinai. It seems obviously so.
The experience of living Judaism as justification for the givens assumed by the Judaism lived.
Speaking for myself. I do believe a philosophical proof does exist. But, just to frustrate the Rambam, I don't think we could identify it. We have too many of what Mussarists call "negi'os", personal ulterior motives, that color our vision. Our ideas of what is a self-evident given that could be used as a postulate for an argument start getting subjective as soon as we go much beyond "x = x". Similarly, our sense of which questions refute the whole argument or are interesting little side challenges that could be shelved for later. They all are so colored by what we want the answer to be that a person couldn't identify a solid argument for or against their position.
Not when dealing with something we are so emotionally invested in as a question that changes how we live our lives.
Or, to rephrase as a Truism:
The mind is a wonderful organ
for proving conclusions
the heart already reached.
