Most think the two witnesses will be Moses and Elijah, and they may be right. We are not told who these two will be. But I think they will be the two prophets that did not see a physical death here on earth. This is Enoch and Elijah. After their 3.5 year ministry of preaching the Gospel to the world, they will lose their powers and will be murdered by this world. This is when they will see their physical deaths. This will also separate the sheep from the goats.
Everything I have said here is just my opinion and is NOT in the scriptures. Thanks.