Can "knowledge about" also be primary experience?
I don't think so, cornelis. "Knowledge about" refers to something that has been "mediated" (analyzed) by the mind. That which is mediated cannot be primary. For example, we may know what a circle is. But since no true circles really exist in nature, they are not given to us from primary experience, but from analyzing the concept of the circle, usually as something that has been taught to us. Thus, our knowledge of the circle is knowledge about. It is that knowledge about that lets us perceive things that have the (imperfect) form of a circle in nature.
On the other hand, we might argue that the idea of "circle" is somehow innate to the human mind (which, after all, is a part of nature). If that were the case, we'd have to dredge it up from the unconscious into consciousness in order to have a "primary experience" of it. It seems to me the dredging operation in this case must be an operation of the mind. So, again, "circle" wouldn't be a primary experience, strictly speaking.
Does this make any sense? Just because I can't think of anything that is "knowledge about" that is also a primary experience doesn't mean there aren't any of those. I just haven't found one yet. Maybe mathematical objects are somehow "primary" in themselves. But it still seems to me that they are useless to us, unless we analyze them and discover the relations that make them what they are.
Can you think of an example of something that can be classed as "knowledge about" that also is a primary experience? I'd be glad to find one!