Did Jesus or any of his disciples ask a deceased person to pray for them?
Obviously Jesus did not, though He did - I suppose - "pray" in a certain way to Moses and Elijah. After Jesus, the Christians constructed their altars over the bones of the Apostles and Martyrs. That contributes to the imagery of the Book of Revelation: "when he broke open the fifth seal, I saw underneath the altar the souls of those who had been slaughtered because of the witness they bore to the word of God" (6:9). Since the Catholic Mass is concieved by the Church as a union of Heavenly and Earthly worship, the saints in Heaven are being depicted as part of the Church.
In the construction of the ancient altars, then, there is a sense of praying
with the Saints who had gone before. Since they are still members of Christ's Body, we still ask them to pray for us.
That is why today's prayer for the Solemnity of All Saints begins: "I saw a vast crowd of countless numbers from every nation, standing before the throne." And later, we recite Revelation 4:11; 5:9,10,12:
"O Lord our God, you are worthy to receive glory and honor and power.
For you have created all things; by your will they came to be and were made.
Worthy are you, O Lord, to receive the scroll and break open its seals.
For you were slain; with your blood you purchased for God men of every race and tongue, of every people and nation.
You made of them a kingdom, and priests to serve our God, and they shall reign on the earth.
Worthy is the Lamb that was slain to receive power and riches, wisdom and strength, honor and glory and praise."
I search the Scriptures to see if what someone says is true. But if you are not Sola Scriptura, how do you know if what you are told is true?
Your quotation of Acts is irrelevent because the Beroeans do not do what you want me to do. The Beroeans searched only the Old Testament (and, curiosly enough, they would have used the Alexandrian Canon - the 45 books in the Catholic Canon of the Old Testament - not your canon). You want me to search the entirety of the Scriptures, both Old and New, and trust myself to interpret it correctly.
When you ask how I know what I am told is true, my answer is that I trust the Church. After all, the Galatians searched the Scriptures, and trusted they knew that the Church was wrong; the Law must be followed. St. Paul condemns this view, and cites his authority: "but even if we or an angel from heaven should preach a gospel other than the one that we preached to you, let that one be accursed!" (1:8).
You want me to trust myself to come up with correct doctrine. I'm too stupid to be able to do so. When the Calvinist and the Arminian can look at the same texts - each claiming that they are "searching the Scriptures" and being led to their conclusion - and be so entirely contrary, I cannot trust myself to be able to figure out God, and God knows that. Because despite whatever you say, you are not searching only the Scriptures to find out what you believe. So, He gave a Church to interpret and to guide.