TKAM is a fantastic novel! I loved studying it

Well first of all I'd definitely start by learning a bit about the context of the novel, do some research about Harper Lee and where she grew up (it's relevant) and also about the culture of the South circa 1930s. This should give you some background and a better idea reading the novel
After that, I'd probably read the novel, not taking notes or anything just reading and getting a sense of the plot, themes and style. After the initial reading, I'd read it again but this time annotate and pick out things you think are important. I do it in my actual book but others type up their annotations.
annotations could be about characters and important things they say, motifs, symbols, themes, literary devices, that kind of thing
That's definitely a good start for the holidays, and whilst I haven't seen Witness, I'd probably repeat the process for any text
good luck!