Did Dobby know about Horcruxes during/before Chamber of Secrets?

Question

“Albus Dumbledore is the greatest headmaster Hogwarts has ever had. Dobby knows it, sir. Dobby has heard Dumbledore’s powers rival those of He-Who-Must-Not-Be-Named at the height of his strength. But, sir” — Dobby’s voice dropped to an urgent whisper — “there are powers Dumbledore doesn’t... powers no decent wizard...” (Chamber of Secrets, Chapter 2 "Dobby’s Warning")

This sounds to me like Dobby is referring to the Horcruxes (what other powers would Dumbledore not have, that no decent wizard touches?)

Is there any canon/JKR support to confirm or reject this guess?

Answer 1

I don't think Dobby was referring to Horcruxes. Dumbledore himself tells Harry that he didn't clue in on Horcruxes as the issue until the end of Chamber of Secrets. This part I addressed in your question Why Didn't Dumbledore Seek Out the Horcruxes Earlier a while ago, so I won't rewrite all that here. The important thing is Dumbledore didn't begin to suspect Horcruxes until after the diary was destroyed at the end of Harry's second year. Quick quote:

Dumbledore paused for a moment, marshalling his thoughts, and then said, ‘Four years ago, I received what I considered certain proof that Voldemort had split his soul.’

‘Where?’ asked Harry. ‘How?’

‘You handed it to me, Harry,’ said Dumbledore. ‘The diary, Riddle’s diary, the one giving instructions on how to reopen the Chamber of Secrets.’

_{Half-Blood Prince - page 467 - Bloomsbury - Chapter 23, Horcruxes}

In that same chapter Dumbledore explains that Voldemort told Lucius that the diary would reopen the Chamber of Secrets, but he did not go so far as to tell Lucius that the diary was a Horcrux. This is supported in Goblet of Fire, when Voldemort says, "I, who have gone further than anybody along the path that leads to immortality." and Dumbledore reminds Harry, "That was what you told me he said. 'Further than anybody.' And I thought I knew what that meant, though the Death Eaters did not."

If Dumbledore did not know of the existence of the Horcrux(es) until the end of Harry's second year -- and did not have absolute confirmation of this until Half-Blood Prince after viewing Slughorn's memory of his conversation about Horcruxes with Tom Riddle -- I can't imagine that Dobby knew about them. Especially as Lucius did not know of their existence.

There is no canon or JKR evidence that I know of that confirms or denies outright the idea that Dobby knew that Voldemort had created Horcruxes. It seems more logical that he just knew about the Chamber of Secrets, likely from overhearing information he shouldn't have at Malfoy Manor. After all, he did have awfully big ears!

Answer 2

There are any number of numerous dark magic "powers" i.e. spells, potions, etc. that Dumbledore would not touch other than the Horcruxes. From the Sorcerer's Stone:

"You flatter me," said Dumbledore calmly. "Voldemort had powers I will never have."

"Only because you're too -- well -- noble to use them."

That being said, Dobby was probably aware of as much as his master was aware, which Dumbledore explains in The Half Blood Prince:(emphasis mine)

Of course, Lucius did not know what the diary really was. I understand that Voldemort had told him the diary would cause the Chamber of Secrets to reopen because it was cleverly enchanted. Had Lucius known he held a portion of his masters soul in his hands, he would undoubtedly have treated it with more reverence — but instead he went ahead and carried out the old plan for his own ends.

I think essentially that this was all of the information that Dobby had to go on, which was enough for him to warn Harry that he was in danger, since the Chamber of Secrets would be reopened. Certainly opening the Chamber and setting the monster within on muggle borns qualifies as a "power" that "no decent wizard" would use.

Answer 3

Consider the Unforgiveable Curses - there are clearly lots of very dark magics that Dumbledore wont use. The Horcruxes are merely the most evil of those that we've seen.

However, Rowling is known to have planned out the entire series in advance - it's very likely that she would have dropped subtle clues throughout.