Hello Tom,
I can't seem to locate this witness, it appears that I have assumed that it's there. So other than that its nature is witnessing I can't say much.
It has the quality of being aware of the sense input and mental activity.
Okay, so see that any reference to an entitiy, a person or separate witness is an inference or a thought. But none of those are actual or findable in any way shape or form.
The only experience you have of "space" are the object appearing in it. Without those object you would be able to perceive space. So space is there but never you see it directly.
If it helps think like a spacelike awareness or like being aware of space.
Awareness is obviously aware as experiencing proves it BUT it is not a "thing" itself. Awareness is not itself an object to be seen, felt, touched, smelled, tasted, or thought.
In DE, I would have to say that I am referring to the one that is aware. It's still hard to look past that I am not the body. It seems like the witnessing is happening through the body, or so I have assumed at least. So it seems to be tightly connected and intimate with my core. Perhaps because it has been there for so long.
The only experience you have of "a body" is sensation.
Where do sensations appear?
Try this:
Introductory Body Exercise
Sit with eyes closed for about 15 minutes.
Paying attention only to the pure sensations, without relying on thoughts or mental images:
Can it be known how tall the body is?
Does the body have a weight or volume?
In the actual experience does the body have a shape or a form?
Is there a boundary between the body and the clothing?
Is there a boundary between the body and the chair?
Is there an inside or an outside?
If there is an inside - the inside of what exactly?
If there is an outside - the outside of what exactly?
What does the word/label ‘body’ ACTUALLY refer to?
What is the ACTUAL experience of the body?
Look very carefully, especially with the last question. Take your time, don’t rush. You can look several times during the day while doing other things (like washing hands, showering, having a short break from work, walking, etc) before replying.