"Who did this?"
Translation:Ai đã làm việc này?
it can't be just này, it doesn't make sense because it is a determiner and, unlike the English pronoun this that can stand by itself, it has to follow the noun it modifies. you got to have "việc này", "cái này", "điều này" like many have suggested, to convey the same meaning as the English this.
I think you would be understood by VNmese anyway.
But there's a slight difference in the meaning of the sentence, according to which one you use:
- việc : something we must do or put effort to. Refers to an action, a task, a chore, business stuff, things to do.
- điều : refers to a thing one is thinking of, talking about or mentioning, like the topic or abstract stuff we were talking about in the last sentence.
In this case we don't have enough context to decide which one to use. However, "most of the times, you can use điều where việc is, but not vice versa".
Another interesting link here