How did the journalist, Upton Sinclair, in The Jungle evoke empathy in people? Provide direct evidence from the text!

According to the Cambridge Dictionary, empathy is

the ability to share someone else's feelings or experiences by imagining what it would be like to be in that person's situation.

Upton Sinclair evokes empathy first, by creating goodhearted "everyman" characters that readers can relate to and identify with, second, by showing situations in which these characters are taken advantage of and treated unfairly, and third, through use of vivid imagery that helps us feel their plight.
It is hard not to feel for Jurgis and Ona and their families as they innocently arrive in Chicago hoping to build a better life for themselves through hard work and staying together. When we first meet Ona, she is brimming with innocence and joy at her wedding:

her happiness painful to look upon. There was a light of wonder in her eyes and her lids trembled, and her otherwise wan little face was flushed. She wore a muslin dress, conspicuously white, and a stiff little veil coming to her shoulders. There were five pink paper roses twisted in the veil, and eleven bright green rose leaves. . . . She was so young—not quite sixteen—and small for her age, a mere child . . .

Jurgis, her new husband, is big and strong and determined to take care of Ona and the rest of their family. He works very hard and is willing to keep on doing so to support dependents. He is no shirker, and will do whatever it takes to earn a living. As he constantly tells Ona:

"I will work harder!"

When Jurgis and Ona and their ten relatives want to buy a house so they can get out of the tenements, we also identify with them. After all, owning one's own home is the American Dream. Further, their goals are modest: a simple four room home for twelve people. Jurgis wants to take care of others and decides:

He would work all day, and all night, too, if need be; he would never rest until the house was paid for and his people had a home. So he told them, and so in the end the decision was made.

Sinclair shows that Ona and Jurgis are good people who deserve a decent life. Ona is kindhearted and gentle; Jurgis is protective, strong, and generous. Yet the novel also reveals how the capitalist order has stacked the deck against them so they can't get ahead. This is the second way he builds our empathy. Their house, for example, is poorly built and cold, and their mortgage contract, which they did not understand, included hidden interest payments. Also, they will lose the house if they miss even one payment. It takes four adults working, and later more and more of the children working, to keep them barely afloat. We feel for this family. They are trying so hard. We experience their pain when Jurgis gets injured on the job and can't work at a time there was no unemployment insurance, when gentle Ona is raped by her boss, and when their little son Antanas drowns in a puddle because there is no one to watch him. Although it is foolish for him to do so, we even understand why Jurgis would beat up Connor for raping Ona.
As shown, Sinclair builds our empathy by creating characters who are like us and then illustrating how they suffer unfairly. Any of us can imagine being Jurgis and Ona, and therefore we take their side when they can't afford to live. As Sinclair puts it:

This was in truth not living; it was scarcely even existing, and they felt that it was too little for the price they paid. They were willing to work all the time; and when people did their best, ought they not to be able to keep alive?

Sinclair's commentary on his characters' plight also uses vivid imagery that helps us feel with our five senses how hard their lives are. Imagery is describing using sight, sound, taste, touch, and smell. Strong use of descriptive detail builds empathy.
Sinclair's narrator uses imagery to comment when he writes of Jurgis:

Day after day he roamed about in the arctic cold, his soul filled full of bitterness and despair. He saw the world of civilization then more plainly than ever he had seen it before; a world in which nothing counted but brutal might, an order devised by those who possessed it for the subjugation of those who did not.

The words "arctic cold" allow us to feel how cold the weather is, but it also reflects Jurgis's bitter soul. We can imagine a snowy wasteland chilling us to the bone inside and out and empathize with Jurgis in physical and emotional distress.
In another passage, Sinclair uses the image of a prison to describe how it feels to be left out of any possibility of obtaining the things you need.

There is one kind of prison where the man is behind bars, and everything that he desires is outside; and there is another kind where the things are behind the bars, and the man is outside.

We can imagine how frustrating and lonely it would feel to see the things you need just out of reach, as if behind prison bars, and not be able to get to them.
Sinclair's novel is sentimental: it unabashedly wants to tug at our heartstrings through idealized characters who suffer terrible events through no fault of their own. This builds our empathy. He reinforces his message and our sense of identification through his use of vivid imagery.