"But I do not know how to do it with a knife!"
Translation:Já to ale nožem udělat neumím!
It can definitely be first, too, but doesn't have to. There are many possible word orders here: "Ale já to udělat nožem neumím.", "Já to ale nožem udělat neumím.", "Ale neumím to udělat nožem.", "Neumím to ale udělat nožem.", "Ale nožem to udělat neumím.", "Nožem to ale udělat neumím.", "Ale udělat to nožem neumím.", "Udělat to nožem ale neumím." ...and more.
Yes, it is a little weird. Actually, German does it, too: "Das kann ich aber nicht machen." (But I can't do that.) So it may be part of the Central-European Sprachbund :) I don't know which other Slavic languages can do it, Slovak can, for sure. PavelBotyg in the comment below says that Russian can't.
Thanks for the explanation! Actually in my e-mail I received two other responses that seem to have been deleted, but which contained useful information.
Firstly, 'ale' takes a zero position in the sentence (I forgot about that.
Consequentely, "ale udělat to nožem neumím" should work, but I had tried that too and it wasn't accepted. I didn't report it, since I wasn't sure.