In Roughing It, chapter 60, I found this:

"But the aggravating circumstance was that these “Greasers” knew that there must be more gold where that boulder came from,..."
So, besides the "N" word occurring here and there in Twain's writings, we also have at least one instance of the "G" word; but it is in quotation marks - I don't recall that ever being the case withe the "N" word.
Does "quotarizing" the slur soften it? Is it less offensive framed that way? - B. Clay Shannon