In my last post I wrote that "We know what we are doing not only better than others know but in a different way. In fact, we know with such certainty that it almost makes no sense to say that we know it. But the chalk example shows that we can be wrong, and so knowledge claims do make sense. There is something that could be true or false, something to know or fail to know." I'm not happy with this for various reasons. It sounds too much like a kind of Wittgensteinian theory to me, and I don't think it's all that true to how we use the word 'know.'
"I know what I'm doing" is usually a defensive remark made to counter a suggestion either that you are incompetent or that your goal is not a wise one. It might be said in answer to "Are you sure you want to climb that ladder in this high wind?" or "Isn't that too much salt?" It isn't something you would normally say unless challenged. So it isn't a simple statement of fact.
What is a fact is that we are normally perfectly able to say what we are doing and that what we say is authoritative. Am I playing a tune with the squeaky pump, or pumping water with it, or murdering the Nazis hiding inside the house? There is a sense in which only I know the answer to this or, rather, there can be circumstances in which only I know the answer. Sometimes the evidence will make it very clear what I was doing, but sometimes it won't.
Performing an action is like acting (in charades, say). Sometimes we need the actor to tell us what s/he (can we invent the word 'acter' so that we don't have to say actor/actress any more?) was doing. But then there is no possibility of a mistake on the actor's part.
If the meaning of, or reason for, your movements is obscure to others then you can remove this mystery by telling them what you are (or at least take yourself to be) doing. In that sense you know what you are doing. But you don't know in the sense of having found out. Nor do you know in the sense that your belief is by definition true. So it might be best not to say that people have knowledge in such cases. As long as we don't get too preachy in the face of perfectly functional cases of ordinary use.