How are the two witnesses killed and raised again?
The two witnesses are killed by the beast that rises from the bottomless pit once they finish their three and a half year testimony, and after their bodies lie in the streets of Jerusalem for three and a half days, the Spirit of life from God enters them, they stand up, and they are called up to heaven in a cloud before the eyes of their enemies.
Scripture shows that the two witnesses prophesy for 1,260 days, clothed in sackcloth, with power to shut heaven so it does not rain, to turn water to blood, and to strike the earth with plagues, much like Elijah and Moses did in the Old Testament. When they finish this testimony, the beast that ascends out of the bottomless pit makes war against them, overcomes them, and kills them. Their dead bodies are left lying in the street of the great city, called spiritually Sodom and Egypt, which is identified as the place where the Lord was crucified, that is, Jerusalem. People from every nation, kindred, tongue, and people look on their bodies for three and a half days, and the world is so glad they are dead that they refuse to let them be buried and even celebrate by sending gifts to one another, because these two prophets had tormented them.
After those three and a half days, the Spirit of life from God enters into the two witnesses, and they stand up on their feet. Great fear falls on everyone who sees this happen. A great voice from heaven calls to them, "Come up hither," and they ascend up to heaven in a cloud while their enemies watch. At that same hour, a great earthquake strikes, and a tenth part of the city falls; seven thousand people are killed in it, and the survivors are frightened and give glory to the God of heaven.
This whole episode ties the ministry of the two witnesses to the pattern of Elijah, who shut up the heavens so it would not rain, and to Moses, who turned the waters of the Nile to blood, showing that God gives these two prophets the same kind of authority in the last days. Their death, resurrection, and ascension happen publicly in Jerusalem, in full view of the nations, and mark the transition into the sounding of the seventh trumpet.
The scriptures
And I will give power unto my two witnesses, and they shall prophesy a thousand two hundred and threescore days, clothed in sackcloth. These are the two olive trees, and the two candlesticks standing before the God of the earth. And if any man will hurt them, fire proceedeth out of their mouth, and devoureth their enemies: and if any man will hurt them, he must in this manner be killed. These have power to shut heaven, that it rain not in the days of their prophecy: and have power over waters to turn them to blood, and to smite the earth with all plagues, as often as they will. And when they shall have finished their testimony, the beast that ascendeth out of the bottomless pit shall make war against them, and shall overcome them, and kill them. And their dead bodies shall lie in the street of the great city, which spiritually is called Sodom and Egypt, where also our Lord was crucified. And they of the people and kindreds and tongues and nations shall see their dead bodies three days and an half, and shall not suffer their dead bodies to be put in graves. And they that dwell upon the earth shall rejoice over them, and make merry, and shall send gifts one to another; because these two prophets tormented them that dwelt on the earth. And after three days and an half the Spirit of life from God entered into them, and they stood upon their feet; and great fear fell upon them which saw them. And they heard a great voice from heaven saying unto them, Come up hither. And they ascended up to heaven in a cloud; and their enemies beheld them. And the same hour was there a great earthquake, and the tenth part of the city fell, and in the earthquake were slain of men seven thousand: and the remnant were affrighted, and gave glory to the God of heaven.
And two olive trees by it, one upon the right side of the bowl, and the other upon the left side thereof.
Then answered I, and said unto him, What are these two olive trees upon the right side of the candlestick and upon the left side thereof? And I answered again, and said unto him, What be these two olive branches which through the two golden pipes empty the golden oil out of themselves? And he answered me and said, Knowest thou not what these be? And I said, No, my lord. Then said he, These are the two anointed ones, that stand by the LORD of the whole earth.
And Elijah the Tishbite, who was of the inhabitants of Gilead, said unto Ahab, As the LORD God of Israel liveth, before whom I stand, there shall not be dew nor rain these years, but according to my word.
And Elijah said, As the LORD of hosts liveth, before whom I stand, I will surely shew myself unto him to day.
And Moses and Aaron did so, as the LORD commanded; and he lifted up the rod, and smote the waters that were in the river, in the sight of Pharaoh, and in the sight of his servants; and all the waters that were in the river were turned to blood.
From the books
This answer is drawn from these passages in the Mary Banks Faith Library.