What exactly is acknowledgement here?
Reference is to On Certainty.
The context is about "justification" of our knowledge: justification cannot go on forever, in search for an absolute ground. It must stop somewhere (compare with The Problem of Induction, and OC, 135).
105. All testing, all confirmation and disconfirmation of a hypothesis takes place already within a system. And this system is not a more or less arbitrary and doubtful point of departure for all our arguments: no, it belongs to the essence of what we call an argument. The system is not so much the point of departure, as the element in which arguments have their life.
110. What counts as its test? - "But is this an adequate test? And, if so, must it not be recognizable as such in logic?" - As if giving grounds did not come to an end sometime. But the end is not an ungrounded presupposition: it is an ungrounded way of acting.
153. No one ever taught me that my hands don't disappear when I am not paying attention to them. Nor can I be said to presuppose the truth of this proposition in my assertions etc., (as if they rested on it) while it only gets sense from the rest of our procedure of asserting.
160. The child learns by believing the adult. Doubt comes after belief.
161. I learned an enormous amount and accepted it on human authority, and then I found some things confirmed or disconfirmed by my own experience.