This is based on opinion. Please don't list it on a work's trope example list.
Tear Jerker / The Emigrants
The deaths of Anna, baby Eva, Arvid, Robert and Kristina.
Karl Oskar's reaction to Kristina's death.
It was also quite the Tear Jerker to realise that Kristina was everything to Karl Oskar yet he got to spend less than twenty years with her and dies at the age of 67. That's almost fifty years without her.
The way the book deals with the subject of leaving everyone you love and everything you've ever known behind. The portrayal of Kristina's homesickness is heartbreaking.
"Home - to Kristina, this encompassed all that she was never to see again."
The details from Anna's death. Hearing her beg her parents to forgive her so that the pain will stop (and asking her father why it hurts so much to die) is gut-wrenching.
When Kristina is so ill from scurvy that she might die and Karl Oskar keeps watch by her side through the night. The things they say to each other and the guilt that plagues him are gut-wrenching.
In Unto a Good Land there's a chapter where Karl Oskar gets lost in the woods on his way home from Stillwater where he went to buy flour so they can have bread on the table. It's mid-winter and one point he passes out from cold and exhaustion and has a rather disturbing dream in which his father reproaches him for the decision to emigrate. This quote from when he answers his father is heartbreaking:
"It wasn't because I was stubborn and wouldn't listen to you, nor was I dissatisfied. That you must remember! I didn't emigrate because of this, do you hear me, Father and Mother? I didn't want to make any more coffins. No coffins for my little ones. Remember that! That was why I emigrated."
The entire chapter about Starkodder the ox.
Kristina's despair when she has her crisis of faith.
The way Max von Sydow and Liv Ullman play Kristina's death scene breaks the heart.
As does, for that matter, von Sydow's performance in the scene where Kristina is bleeding from every orifice due to scurvy.
Also during the crossing of the Atlantic, Fina Kajsa when they come to take her dead husband away.
Ljusa kvällar om våren (Bright Evenings in Springtime) where Kristina sings about how homesick she is.
Gold Can Turn To Sand.
"As his eyes slowly faded, the old watch fell from his hand, and Kristina, gold had turned to sand..."