The word appears 5 times.
You will need to read the Wikipedia entry on this as I have no plans to read thie 7 volume novel. However - I can say it was written starting in 1909 so the word was still common. In such a large work, perhaps it is surprising that it does not appear more often.
"I've no intention of making fun, I assure you. Well, to continue, she went up to one of these black fellows with 'Good morning, nigger!' "
"Oh, it's too absurd!"
"Anyhow, this classification seems to have displeased the black. 'Me nigger,' he shouted (quite furious, don't you know), to Mme. Blatin, 'me nigger; you, old cow!'"
"I do think that's so delightful! I adore that story. Do say it's a good one. Can't you see old Blatin standing there, and hearing him: 'Me nigger; you, old cow'?" I expressed and intense desire to go there and see these Cingalese, one of who called Mme. Blatin and old cow.
"Oh-yow-yow! Tut-tut-tut-tut. Did you ever! Why, it must be that woman we saw - you remember, Leader, - we said at the time we didn't at all like the look of her, but we didn't know it was the 'Marquise' sheid com to see. A woman with a nigger-boy, you mean?"
"That's the one."
"D'you mean to say so? You don't happen to know her name?"
"Yes, I made a mistake on purpose; I picked up her card; she tradesunder the name of 'Princesse de Luxembourg!' Wasn't I right to have my doubts about her."