What kind of lesson is Mr. Pocket supposed to give Pip?
Mr. Matthew Pocket (Herbert's father) is supposed to be something of a general tutor for Pip. We are not told that he is supposed to be giving Pip any particular kinds of lessons. Instead, he is just supposed to be teaching him general things that he needs to know.
I think that the best place to find this answer is right at the beginning of Chapter 24. At that point, Pip says that he has found out that he is not supposed to be learning any particular profession. So Mr. Pocket is not meant to be teaching him how to do some particular job. Instead, Mr. Pocket is just supposed to teach Pip stuff that he needs to know in order to "hold (his) own" among young gentlemen.
I take that to mean that Pip is just supposed to be getting a decent basic education so that he will not look like an idiot when talking to people of his age and class.