Questions & Answers about Kto pije to piwo?
Why do we use the "he/she/it" form of the verb (pije) after kto?
In Polish, the question word kto (who) always takes the third-person singular verb form, just like "he" or "she". That's why we use pije (he/she/it drinks) instead of a plural form like piją (they drink), even if you suspect multiple people might be drinking.
Since the beer is the object being drunk, shouldn't piwo change its ending?
You are right to think about the object case (the accusative) here! However, piwo is a neuter noun because it ends in -o. A very helpful rule in Polish is that neuter nouns look exactly the same when they are the object of a sentence as they do in their basic dictionary form.
Why do we say to piwo instead of ten piwo or ta piwo?
Words like "this" have to match the gender of the noun they describe. Because piwo is a neuter noun, we must use the neuter form to. If the noun were masculine, we would use ten, and if it were feminine, we would use ta.
Does this sentence mean "Who drinks this beer?" or "Who is drinking this beer?"
It can mean both! Polish does not have a separate "is doing" (continuous) tense like English does. Depending on what is happening in the moment, Kto pije to piwo? translates perfectly to either "Who usually drinks this beer?" or "Who is drinking this beer right now?"