On page 118 of Thomas King's Medicine River, we see the word borrowed surrounded in quotation marks: "borrowed." So, it seems that in your question, you actually meant to ask why borrowed is surrounded in quotation marks rather than question marks. The only reason I can think of that you might personally be seeing the word in question marks is if you are using some sort of e-version of the text and not all of the characters are showing up as they need to be, leading to typos. So, let's discuss exactly what it means to surround this word as well as any word in quotation marks.
The sample passage pertaining to your question describes a character as having "'borrowed'" a car the night he graduated and winding up in a car accident:
... But on graduation night, he took off with a couple of friends, "borrowed" a car, and drove it to Edmonton, where they wrecked it after a high-speed chase with the cops. (p. 118)
A standard punctuation device a writer can employ is surrounding single words or phrases in quotation marks to create specific meaning, even when the words or phrases are not being directly quoted as being said by someone else. More specifically, we can use quotation marks around single words and phrases to create a special effect. Using quotation marks in this way shows that we are "using that word in a special or peculiar way and that [we] really mean something else" (Capital Community College Foundation, "Quotation Marks"). In other words, it's a way of indicating we are using the word to mean something beyond the standard dictionary entry. Another way to explain this is that we are using the word in a non-literal, ironic, and even sarcastic sense. Washington State University, in the article "Quotation Marks," gives us the sample sentence:
She ran around with a bunch of "intellectuals."
Here, the writer is being sarcastic when the writer uses intellectuals and actually means the exact opposite--the "she" in the sentence literally associated with a bunch of idiots, not intellectuals.
So, looking again at our own sample passage, King chose to surround the word borrowed in quotation marks because he is not using it literally. The character did not literally borrow a car in the proper sense, meaning that the character asked the owner permission and had every intention of returning it in its original condition. Instead, the character literally stole the car, which resulted in running from the police and a car accident. Hence, we see that King, based on a standard punctuation rule, is using the word borrowed ironically or sarcastically.