Re: Where should the stress in the sentence be put? Are both variants possible?
You can also use "Tell THEM to give me the knife!" If there were two sets of people, both with a knife and you wanted to direct someone else to tell one of those groups to give you their knife, you would say that probably while pointing towards the group you meant. You would be stressing "THEM" to emphasis "that group" not "the other group".
Remember - correct capitalisation, punctuation and spacing make posts much easier to read.