What major events take place in this Chapter 16 of To Kill a Mockingbird?
The study guide for Lee's novel gives a full answer to your question. It identifies three new characters that are introduced, including Dolphus Raymond, who's discussed in the previous post. It also gives a summary and a discussion; both are worth checking out.
I'll add that what I find most interesting about this chapter are the pre-trial festivities (it's a "gala occasion," the novel tells us); Jem, Dill, and Scout's discussion of the "one-drop rule"; and the segregation of the blacks both outside and inside the courthouse. Jem, Dill, and Scout sit in the balcony with the black spectators, but they aren't there as equals. Black people seated in the front row of the balcony stand, giving up their seats to the white kids in a gesture that reminds me of the Jim Crow rules that lead up to the Montgomery Bus Boycott in the mid-1950s.
One of the biggest events in Chapter 16 of To Kill a Mockingbird is the beginning of the trial. People come from all over to watch the trial of Tom Robinson, a black man accused of raping Mayella Ewell, a southern white girl. Wagon loads of families arrive. People bring picnic meals and it is almost like a circus and seems to be entertaining for the crowd. Atticus is a lawyer who is defending Tom. His children Jem and Scout try to sneak into the trial and end up in the available seats in the balcony, the only section where black people may sit due to segregation.
Dolphus Raymond, a man in the town who has black female partner and children who are bi-racial, mulatto, is discussed by Jem and Scout. They try to determine why the townspeople refer to him as trash. Despite the fact that the man came from money and owns property he is still considered to be trash by the townspeople. The children also discuss the views of the era about bi-racial "mixed" children. The discussion indicates that the children do not fit in with the black race and are not wanted and they are not wanted by the white race.