"Who is--or who was--the hooded woman with the owl? Do you know?"
"Well!" said Ikey, holding up his cap with one hand while he scratched his head with the other, "they say, in general, that she was murdered, and the howl he 'ooted the while."
This very concise summary of the facts was all I could learn, except that a young man, as hearty and likely a young man as ever I see, had been took with fits and held down in 'em, after seeing the hooded woman. Also, that a personage, dimly described as "a hold chap, a sort of one-eyed tramp, answering to the name of Joby, unless you challenged him as Greenwood, and then he said, 'Why not? and even if so, mind your own business,'" had encountered the hooded woman, a matter of five or six times. But, I was not materially assisted by these witnesses: inasmuch as the first was in California, and the last was, as Ikey said (and he was confirmed by the landlord), Anywheres.
That sentence is a bit confusing because it consists of several dependent clauses strung together with commas. (Not that I'm criticizing the writing of Charles Dickens ;-)
Basically, the subject and predicate are: "... a personage ...had encountered the hooded woman, a matter of five or six times."
The "personage" (or person) had been "dimly described as 'a hold chap, a sort of one-eyed tramp, answering to the name of Joby'".
Further, if you called him Greenwood (apparently his family name), Joby would reply 'Why not? and even if so, mind your own business...'. Dickens uses the phrase "challenged him" for "called him", which would not be commonly used in modern English, but perhaps was in Dickens's day?
So Dickens is putting quite a lot of background information about Joby Greenwood into the same sentence where he is basically just saying that 'Joby Greenwood saw the hooded woman five or six times.'
Rumour had it that the hooded woman, had been met five or six times by a(n) (h)old man with one eye, poorly dressed like he slept on the streets. This person's name was likely Joby Greenwood, but if you confronted him with "Are you Greenwood" he would answer "Why not? and even if so, mind your own business"
Hold could, as mentioned by Peter Shor in a comment, be old with an H added as some dialects do or possibly be
A carcase, dead body, corpse.OED