The one where we discuss Beorn & berzerkers & eagles & Russian novels and what a queer thing man is, what a queer thing language is, and what one has to do with the other. And also totemistic bear spirits.

Did Tolkien read Dostoevsky? The protagonist in Dostoevsky's “The Double” is a fellow named Golyadkin (Голядкин); a neurotic individual on the verge of a nervous breakdown who has conversations with himself very similar to Gollum/Smeagol in Tolkien's "Lord of the Rings".  Coincidence?  Golyadkin debaters with himself,

Everything, apparently, and even nature itself, seemed up in arms against Mr. Golyadkin; but he was still on his legs and unconquered; he felt that he was unconquered. He was ready to struggle. he rubbed his hands with such feeling and such energy when he recovered from his first amazement that it could be deduced from his very air that he would not give in. yet the danger was imminent; it was evident; Mr. Golyadkin felt it; but how to grapple with it, with this danger? - that was the question. the thought even flashed through Mr. Golyadkin's mind for a moment, "After all, why not leave it so, simply give up? Why, what is it? Why, it's nothing. I'll keep apart as though it were not I," thought Mr. Golyadkin. "I'll let it all pass; it's not I, and that's all about it; he's separate too, maybe he'll give it up too; he'll hang about, the rascal, he'll hang about. He'll come back and give it up again. Than's how it will be! I'll take it meekly. And, indeed, where is the danger? Come, what danger is there? I should like any one to tell me where the danger lies in this business. It is a trivial affair. An everyday affair. . . ."

Tolkien's Library: An Annotated Checklist by Oronzo Cilli might give answer to this if the good professor had the Russian novel on his shelf (either in Russian or in translation as Tolkien new the Slavic language well).

More likely, though is that It is from Old Norse.

In The Annotated Hobbit with annotations by Douglas Anderson, Anderson claims that Gollum is from the Old Norse gull meaning Gold, and an inflected form of this is gollum meaning; gold, treasure or something precious. In the oldest manuscripts it is spelled goll. One inflected form would be gollum, 'gold, treasure, something precious.' It can also mean 'ring,' as is found in the compound word fingr-gull, 'finger-ring.'"

As for Beorn, Tolkien's original name for this character was “Medwed” (Russian/Slavic: “medved” = “bear”) - which indicates Tolkien knew Slavic.

So the question is still up for debate: did Tolkien read Dostoevsky?