Technically speaking, it is written in the third person since events are narrated using the pronouns of 'he,' 'she,' 'they.' However, often the storyteller crawls into Jonas' brain, so to speak, and relates his thoughts not spoken aloud to others.
If such were the case of all the characters, this would be called the third person omniscient point of view. However, insight into one's thoughts is limited to the character of Jonas, - except of course when the Giver imparts to him a memory.
Levels of conflict are both external and internal in this story, and a lot of what "happens" is on a purely mental basis. You could even create a second plot line if you wanted to, tracing the changes in Jonas' mind-frame from the beginning to the end. It is interesting that the crisis moments are not when something happens but are rather when Jonas actually decides to think and act for himself.
The Giver is written in the third person. Jonas is able to recover memories from the receiver before him, the "Giver". The reason why an author would write a novel in the third person is to be able to get inside several of the charcters' thoughts and reveal them in the narrative. This knowledge helps the reader know several of the characters intimately. For example, we can know them through their thoughts as well as through their dialog and through other characters opinions of them.
It was given in Third Person mode.