Translation:What is the difference between the machines?
We say "Jaký je rozdíl", not *"Co je rozdíl". Czech word order is flexible, when rozdíl is at the end, it is stressed.
Does this Co/Jaky concept apply to only rozdil or are there other examples? Thank you!
If I had gotten this translation from English to Czech, I probably would have written "co." But now, seeing that it's actually "jaký" that is used, I'm reminded of simple sentences earlier in the course such as "Jaká je Kateřina" and "Jaký je František (What is K or F like?). So I'll probably fix this construction in my head as "what is the difference (like) between X and Y." Hopefully, it will work...
Perhaps there are more than two machines. In that case, could you say, "What is the difference among those machines?" since "mezi" can be translated as "between" or "among"?
Possibly, I am not sure. See https://blog.oxforddictionaries.com/2015/06/29/grammar-myths-among-or-between/