How to Know the Knowing of Anicca, Dukkha, Anatta Anicca, dukkha, anatta. I've listened to plenty of bhikkhus and bhikkhunis talk about these characteristics at length.

Take for example anicca. I am asking the same thing about dukkha and anatta.

Suppose one has not yet seen for oneself how all phenomena are impermanent, but has an intellectual understanding of it from listening to the Dhamma.

Is it possible that such a person could, for instance, recognize anicca, but not understand that they have recognized it, thinking, "Anicca is yet to be grasped", when in fact anicca has already been grasped? To clarify, the person might even reap the benefits of understanding anicca. They don't fret about illness, nor about building a career, nor about global warming, for instance. (I have picked a few things from my own life that I am still learning to deal with). Yet the person still thinks, "Anicca is yet to be grasped."

If it is possible, how is it possible and what should one do about it? If it is not possible, why not?

As a guess, does the answer lie in the person's actions?

As another guess, is this a more specific case of asking how to know one's own mind?
There is knowing of Anicca, knowing of Dukkha, and knowing of Anatta, separate from each other. And then there is knowing of all three together, or rather the knowing of vision behind these three designations, in all its implications.

In my experience, it is seeing all implications, top to bottom, is what makes all the difference in the world. I had intellectual understanding of the three marks for years. I even understood shunyata, or thought I did. I even knew that Enlightenment can't be a state. And I still missed the point.

It's all about implications, of all three, together. When you know reality behind the three, and all implications of this reality, then you can be sure you know what is there to be known. Until then, to think "anicca (etc.) is yet to be grasped" would be a valid thought. Why? Because if you don't see how it fits together, or do see how it all fits together but not its implications -- then your knowledge of individual components is obviously not 100% complete yet.