In The Giver, what are the main events that occur in chapters 8 to 15 as part of the rising action?

These events in the rising action include Jonas’s appointment to Receiver of Memory and his training.

The first part of a book, chapters one through seven in this case, is exposition.  Exposition is the part of the book that introduces the main elements, including the characters, setting, and initial conflict.  The middle of a book, chapters eight to fifteen here, makes up the rising action.  Rising action is the important events of a story that occur between the exposition and the climax.  These events lead up to the climax and build suspense and interest.  The climax, of course, is the most exciting part of the book and the turning point of the plot.

At the beginning of the rising action, Jonas is preparing himself for the Ceremony of Twelve.  This is the event that will shape the rest of his life.  He does not know what assignment he will get, because he has never focused on any one area of study.  Jonas is apprehensive and curious.

When Jonas is chosen to be the new Receiver of Memory, it is a shocking moment for him because it comes as just as much a surprise to him as to the reader.  First, Jonas is skipped during the ceremony.  This leads him to believe he must have done something wrong.  It turns out that he was skipped because his is a special appointment that does not happen very often.

"Jonas has not been assigned," she informed the crowd, and his heart sank.

Then she went on. "Jonas has been selected." (Ch. 8)

Everyone in the community seems puzzled.  They must have a very short memory, because Jonas is not the only time a Receiver of Memory has been chosen.  His predecessor Rosemary failed.  Jonas was chosen to replace her ten years later.  The Chief Elder describes the traits that Jonas has that mean he is up to the task: intelligence, integrity, courage, and the Capacity to See Beyond.

Most people have no idea what that last one means, but Jonas has been having strange visions for quite some time now. He has one there, at the ceremony, and confirms that he does have all of the traits listed, including the Capacity to See Beyond.  Jonas gets a list of rules for his assignment, and they confuse and trouble him.  He is told that he can lie, and that he cannot apply for release.  He has no idea what these rules mean.

Jonas begins his training with The Giver.  This is another key event in the rising action.  As Jonas gets more and more training, he learns that the world used to be pretty different.  Before sameness, there was snow and hills.  Jonas takes a ride on a sled, and gets a sunburn.  Both are completely new concepts to him.

"It hurt a lot," Jonas said, "but I'm glad you gave it to me. It was interesting. And now I understand better, what it meant, that there would be pain." (Ch. 11)

Jonas later dreams about the memory, even though before he rarely dreamed.

After talking with his friend Fiona, who seems much changed since she started her training as a Caretaker of the Old, Jonas asks The Giver about the Capacity to See Beyond.  The old man explains that Jonas began to see the color red, as in the apple, Fiona’s hair, the skin tones at the ceremony, and now the sled.  Jonas asks the man if he will ever see all of the colors.

"Of course. When you receive the memories. You have the capacity to see beyond. You'll gain wisdom, then, along with colors. And lots more."  (Ch. 12)

The Giver gives Jonas a special memory of a rainbow.  Soon Jonas can see all of the colors in his everyday life.  He asks The Giver why no one in the community can see colors, and The Giver explains that it is part of Sameness.  With colors come choice, and choice has been mostly eliminated from their lives.  Choosing, even only with colors, would be “not safe” Jonas decides.

Jonas tries to tell Lily that her comfort object, an elephant, was once real.  When she does not believe him he attempts to transmit a memory to her.  It completely fails.  Lily does not have the Capacity to See Beyond.  Jonas tries to find out if The Giver is lonely, because he is starting to realize he is very different from everyone else.  The Giver confides that he lives an isolated life, but tells him that when the last Receiver failed, it was disastrous for the community.  They need him and Jonas, to hold their memories and their pain.  The Giver tells Jonas that his instructors “know nothing” about memory (Ch. 13).

Jonas asks The Giver what causes him pain, and takes the ride on the sled again—this time with a broken bone.  It is like nothing he has ever felt before, and no relief of pain medication can cure it.  Jonas realizes what the pain The Giver has warned him about means.  He also realizes that no one in his community has ever really known pain.

That night, Jonas’s father announces that identical twins are about to be born.  The smaller one will be released.  Jonas is unclear what this means.  He thinks the other twin will be taken somewhere else.  Jonas volunteers to have Gabriel sleep in his room. When he is rubbing the baby's back, he accidentally transmits a memory to him.  Gabriel does have the Capacity to See Beyond, because he, Jonas, and The Giver are related (you can tell by the pale eyes).

The next day, Jonas comes in and finds The Giver in pain.  He agrees to take the memory, and finds himself in the middle of an old fashioned war.  He sees death for the first time, and is horrified and frightened.  The Giver asks Jonas to forgive him.

These events lead up to the climax, when Jonas’s father kills the infant.  It is then that Jonas puts all of the pieces together, and realizes what release means.  That coupled with an argument with Asher about playing war leads Jonas to understand that his people have no concept of death or suffering of any kind, any more than they understand pleasure.  This realization causes him to despise his community and all it stands for.  He plans an escape to return the memories to the people and bring reality to his world.