We are truly awake all the time, as long as life is alive and breathing in our bodies. But to know that we are truly awake is an entirely different thing. For knowing we need to come back to the here and now and start living life wholly. When we experience our aliveness in this moment fully, momentarily we would not only be truly awake, we would also know we are truly awake.
The knowing here is different from the knowing of the thinking mind with respect to the outside world. We learn information and when we understand it and remember it, we say that we know it. But here the knowing does not happen in the same way. Had it been so, then the first sentence of this answer would have been sufficient, isn’t it? I said, “We are truly awake all the time, as long as life is alive and breathing in our bodies”. You read it and now you know it. But still it doesn’t seem to be answering your question.
Because the knowingness needs to arise from within us, our of our own experience. It needs to be a realisation because it is not an information. What do we need to experience? To our thinking mind it seems that the highest thing to realise would be the most complex and difficult thing. Just as a PhD thesis is the most difficult piece of document to read and understand. And there lies the twist. The simplicity of it makes our mind reject it and keep searching.
The only way to experience it is to stop searching. Not only stop searching but also stop striving, wanting, thinking, stop all doing. Just remain quietly in a state of non-doing being. When the thinking mind goes quiet, the aware mind starts becoming perceivable. We begin to be aware of our awareness. Or we begin to be conscious of our consciousness. In that moment, we truly know that we are truly awake. It is momentary and you can keep returning back to that momentary awareness. Why is it momentary? Because of our habitual tendency to go back to living in the thinking-mind. The mind will try to capture even this knowingness into concepts and theories, into words and thoughts. And the knowingness would be lost.
The knowingness is a state of being. Gradually you would be able to cultivate a habit of returning back to this state of being.