"can I try on x" and "can I try x on" are pretty much interchangeable in English. I've been reporting these for months. I really can assure you that I know my mother tongue quite well. PLEASE fix them, it's driving me round the bend because I don't always remember to use Duolingo-English rather than real English :'(
Native English speaker here- I instinctively translated it as "this dress" because if you're asking, you probably have a specific dress with you. I think duo wanted to emphasize that this sentence in Ukrainian doesn't use "це", but this is one of those translations that I can't ever picture an English speaker using in everyday life.