PHNone of them is correct, but the second one comes close.
The sentence should be: “Could I ask a favour of you?”
The first and third sentences are also formally incorrect because they use the preposition “from,” when they should be using “of.”
They all also are not formally correct because they use the modal auxiliary verb “can,” when “could” should be used.
“Can” means, “Am I physically able to …?” while “could” means “Is it possible for me to …?”
The sentence should be: “Could I ask a favour of you?”
The first and third sentences are also formally incorrect because they use the preposition “from,” when they should be using “of.”
They all also are not formally correct because they use the modal auxiliary verb “can,” when “could” should be used.
“Can” means, “Am I physically able to …?” while “could” means “Is it possible for me to …?”