Agreed, but in English the present tense would be, "Who is eating my cookies?" "Who eats my cookies" sounds like someone is taking a poll or needs to know how many people would be eating them (as if to find out how many should be made available in order to ensure that there are enough of them). The Italian sentence doesn't seem to be asking that question... It seems to be asking, "Who is/are the person(s) responsible for eating the cookies." If that's an accurate understanding- then "Who is eating" would be the correct English.
No American would ever say "who eats my cookies" as that imply someone eats your cookies on a regular basis.
If you found out your cookies are gone you'd ask "who ate my cookies?" If someone is eating your cookies at this very moment you should ask "who is eating my cookies".
"who eats my cookies" makes no sense in 99.9% of situations
Both one is correct, but have different meaning.
- "Chi mangia i miei biscotti?"
- "Who eats my cookies?" (third-person singular; only one person does)
- "Chi mangiano i miei biscotti?"
- "Who eat my cookies?" (third-person plural, more people might do it)
Look at the verb conjugation of italian verbs, English omits verb conjugation, so for an English native it might be difficult to learn these constructs.
I'm really struggling for "cookies" as a translation of "biscotti". I've eaten Italian biscuits and all the ones I've had are crunchy i.e. Biscuits, nothing like what I would consider a cookie to be. Now I know that on the other side of the Atlantic the word cookie is used more generically for biscuits, but surely not the really crunchy Italian types?