[Radek]

That's weird. You need not tell Scanthrill anything, just wait. Scanthrill himself will ask whether you have done the "job". Answer "yes" and you get the dagger.
Perhaps, you were little hasty with your keyboard. Try again: be silent and let Scanthrill drivel. He will talk about "payment" first and then he should ask about your proceedings with the "job". The question about completion of the job should invoke a list with "yes", "no", etc. Select your answer from the list.