Much quoted sentence for illustrating scope ambiguity.
"Everyone loves someone" -  here someone can refer to a certain individual or different individual.But if everyone turns into a killer as told by the following sentence.what would happen to the ambiguity
:" everyone kills someone"- Ambiguity disappears,doesn't it- but how.
Could anyone give me an answer?

This is a question of linguistic or encyclopedic meaning/knowledge.

I think that "Everyone kills someone" actually is still ambiguous, linguistically. Imagine a crazy world in which you could kill people multiple times-- or even a not to strange video game. "On level one, everyone [each player] kills someone [the bad guy named 'John']."

This does get into issues of coercion (does the sentence/context force the words to change meaning?) and normal usage. It's very similar to a sentence like "I drank the potato." It's not necessarily incoherent in some ways, but as a whole idea it's wrong. It's unclear whether we want to call that a syntactic or semantic or pragmatic effect! The thing is... in a weird cartoon you could imagine Mickey Mouse drinking a potato, with the right kind of animation. So... what is it? Grammatical?

This is, of course, what Chomsky discussed with "Colorless green ideas sleep furiously."
Personally, I disagree with him. I think that's a perfectly fine (but effectively useless) English sentence; I even think the meaning is coherent, though we as speakers in the real world may not be able to fully comprehend/contextualize it. But, again, think of a cartoon. I could try to draw that!



As for a more specific point about the verb "kill" versus "love", there's an issue of Aktionsart (or Lexical Aspect) including telicity and so forth. In that case, it also just happens that "kill" is a unique event. Technically another verb like "hit" is also similar for Aktionsart and would be unique in each instance, but then there could be unrelated instances. It's sort of a sloppy reading to have "Everyone hit someone" for one person, because that would be multiple hittings. Actually I suppose not-- you could have everyone punch you in the face at the same moment... is that just one hitting? Ha. But then in that case, as PhantomSoul hinted at, you can get that reading fairly easily I think-- "Everyone killed someone by pushing him off of the cliff together". Only the separate events reading is unavailable, actually.

The distinction of whether it's collective or iterative is important, though. Collective killing is coherent (stoning for example), at least when we aren't looking at extremely precise medical details. Iterative killing is bizarre, except in imaginary circumstances (like a video game).
I think this is just a different kind of ambiguity in the sentence, not related to scope. And I'm not sure where it's coming from or what the technical term would be. I suppose it's just related to plural verbs?
Ah, a search turns up the term "collective-distributive ambiguity", which makes sense.

I'm glad to see we have the same intuitions! (...about ... the concept of semantic ill-formedness.)

I find almost anything to be well-formed as long as the structure works, because, for example, it's easy to ask WH-questions about confusing sentences-- "What color were the colorless ideas?" -- "Green!" It's certainly pragmatically incoherent, but semantically I don't see a fundamental problem, no more than something like "I have 10 trillion dollars!" (I don't, by the way...).