Thought is but another 'thing' amongst 'things'. All things are witnessed, if witnessed at all. Even this witnessing can be witnessed, if you pay enough attention.
If a thought is a thing which is a copy of all things... must it also contain within itself a copy of itself? And within that copy of itself within itself... Can this be allowed? Is it not that these things are 'separate' but ... not?
Perhaps we should divide reality into 2 classes of things called perhaps A-Things (things) and B-Things (thoughts) and we are able to perceive both of these 'things', depending on whether we are able to, care to or dare to look at them. A-Things and B-Things do seem to interact, however.
Wait a moment! Perhaps the witnessing 'thing' is another 'thing'! It just works differently, right?
There are so many different things... it's going to take a lot of categorisation to get this entire mess sorted out! If you think I'm going to do all that work, you've got another thing coming!
What's this time thing? Energy? Separation? Alligators in the sewers!!! Was that my phone ringing?
So, are thoughts copies of these things? Or things which reflect (upon the nature of) other things which through the witnessing torch which is held by a monkey, riding a unicycle on a tightrope wearing heavy armour. (Sometimes we fly, though not for long...)
We identify with the thoughts. We call them 'my/our thoughts'. We consider ourselves to be the source of them. The witnessing thing is harder to identify with because it lacks content. It "holds" all things, as we perceive them.
Thoughts, as a particular type of thing, can be faithful reflections or less than faithful ones. They also reflect each other.
There are perhaps different ways of "knowing" and different types of "knowledge". Some being based in thought and some in witnessing. Also, there are other types like musical knowledge, for example. (Look to the many terms for knowledge in languages).
There is probably a lot more to be said on this topic. That'll do for now.