There seems to be several layers of not knowing.
First, there is ourselves as capacity for the world, the Original Face, the void pregnant with potentials. And this manifests as pure awareness and what arises in the present, as the experiencing and the experienced.
The void and the pure awareness are both distinct from abstractions – there is an absence of “knowing” in the sense of abstractions, thoughts, ideas, images etc. here. There is just pure awareness and deep silence, along with what arises in the present.
On the level of abstractions, the not knowing takes the form of intellectual honesty.
Existence is always more than and different from our experience of it. And our experiences are always more than and different from the abstractions drawn from them. There is a world of difference between Existence and the abstractions used to describe our experiences of Existence. The terrain is always different from the map. The description something else than the described.
Any abstraction is a tool of only limited, temporary and pragmatic value. And when we recognize this, it becomes a more useful tool.
If we are honest about this, we see that there is a deep not knowing inherent in any abstraction as well.
This is all pretty obvious, but we often act as if our abstractions and thoughts themselves are the gospel truth. Even people in science often do this, even if it goes against the most basic principle of science.