There have been numerous statements of being Christ's witness over the years. There is a very detailed description given by Lorenzo Snow of when Christ called on him to be the prophet. I believe it was right after his being in the Holy Of Holies begging the Lord to preserve the life of Wilford Woodruff so that he wouold not have to lead the church. Christ told him to call the twelve to gether and reorganize things. That can be found here:
Lorenzo Snow sees Christ Its on page 85, or you can use the scroll on the left and click on "The Savior appeared to him in the Salt Lake Temple." Click on the page to enlarge it to readable size.
I know of an account given by Truman Madsen, it might be in his book regarding the Presidents of the Church, of President McCay's personal secratary testifying of an appearance. A new Apostle needed to be called, and Bro. McCay was stumped. he had a short list, but needed confirmation. He told his secratary that he was going to go to the Lord with the problem and would be back soon. A short time later he was called back to the office. He stated that Bro. McCays face shone like Moses when he came from the mount, and the president said that the Lord had told him who to call, and would he please get the number so that they could call him.
A similar story is told by Bro. McConkie in regards to his calling to be an Apostle. Harold B Lee called him to his office and informed him of his calling. He stated that he had approached the Lord with a list of possible candidates of who should be called. He said that he had argued with God in regards to McConkie being called, but the Lord had insisted. McConkies son asked him if it hurt his feelings that Bro. Lee had argued about the calling, and Bruce said "No, I would rather be called by the Savior to be an Apostle than by a Prophet anyway."
you can add to that his own testimony: "I am one of [Jesus Christ's] witnesses, and in a coming day I shall feel the nail marks in his hands and in his feet and shall wet his feet with my tears. But I shall not know any better then than I know now that he is God's Almighty Son, that he is our Savior and Redeemer, and that salvation comes in and through his atoning blood and in no other way."
Boyd K Packer gave an entire talk on the subject of the brethren being witnesses of the Savior. That talk can be found here:
LinkIn it he states :
Occasionally during the past year I have been asked a question. Usually it comes as a curious, almost an idle, question about the qualifications to stand as a witness for Christ. The question they ask is, “Have you seen Him?”
That is a question that I have never asked of another. I have not asked that question of my brethren in the Quorum, thinking that it would be so sacred and so personal that one would have to have some special inspiration, indeed, some authorization, even to ask it.
There are some things just too sacred to discuss. We know that as it relates to the temples. In our temples, sacred ordinances are performed; sacred experiences are enjoyed. And yet we do not, because of the nature of them, discuss them outside those sacred walls.
It is not that they are secret, but they are sacred; not to be discussed, but to be harbored and to be protected and regarded with the deepest of reverence.
He ends the talk with this statement:
Now, I wonder with you why one such as I should be called to the holy apostleship. There are so many qualifications that I lack. There is so much in my effort to serve that is wanting. As I have pondered on it, I have come to only one single thing, one qualification in which there may be cause, and that is, I have that witness.
I declare to you that I know that Jesus is the Christ. I know that he lives. He was born in the meridian of time. He taught his gospel, was tried, was crucified. He rose on the third day. He was the first fruits of the resurrection. He has a body of flesh and bone. Of this I bear testimony. Of him I am a witness. In the name of Jesus Christ. Amen.
We can easily forgive a child who is afraid of the dark; the real tragedy of life is when men are afraid of the light. - Plato