And can I just say: "哪里买票？"? This is what I used when I was in China and everyone seemed to easily understand. Is this shorter sentence incorrect or non-native sounding? How do native speakers ask this kind of question?
I see some nuances when I use those sentences/phrases.
I would use these sentences '哪里买票'，'在哪里买票'， or '请问, 在哪里买票', when I try to ask where the ticket office(售票处) is. Most likely, I would use '请问, 在哪里买票' because that sounds more polite than the other twos. Those sentences can be paraphrased as (请问)买票的地方在哪里， and they are usually used when you arrive a site(say a station), but you are not sure exactly where the ticket office is located in there.
I would use 哪里可以买票 and 哪里可以买到票, when I am not sure where I should go to get tickets(train station, Internet or any other places). The latter connotes that you are asking for a place where can surely get tickets, the former is just to ask where you can buy tickets but unsure if you can get tickets successfully.
哪里买票 = where can I buy ticket? (tell me somewhere I can try, but you don't have to be 100% sure that I can get the ticket, maybe they sold out, or they are not selling the ticket now, but they were before)
哪里可以买到票 = where can I buy ticket? (you are 100% sure that I can buy a ticket there - but still there might be something happened that I could not get the ticket)