give. Add "power". Figure of speech Ellipsis.App-6.
My two witnesses. God has not specified their names. We know that two men are to be raised up "in that day", endowed with wondrous powers to execute a special mission. They are called emphatically "MY two witnesses "(See Rev_1:5).
prophesy. See Rev_10:11 and App-189.
a thousand . . . days = forty-two months, Rev_11:2. The periods are probably synchronous.