We know that we have what we asked of him.
“If you remain in Me and My words remain in you, ask whatever you want and it will be done for you. My Father is glorified by this: that you produce much fruit and prove to be My disciples. (John 15:7-8) HCSB
Jesus connects answered prayer (exactly what you ask for, not something different) to “proving” one’s discipleship/ or followership. At this point, some suggest that with the last death of the apostles, things like always answered prayer, the greater miracles of Jesus and the gifts have ceased. However, this conclusion is based of atheism/empiricism, not Scripture. Jesus did not say, “if the apostles are still alive, and their words abide in you, then ask for what you wish.” If that was the case, then because the apostles are gone, then logically the greater miracles and always answered prayer are gone for me. Not only is that not what Jesus said, but it makes man the focus. It habitually makes man the center. When I do deduction from scripture and apply them to myself, Jesus is my major premise not men. Jesus is my deduction for my reconciliation, answered prayers, greater miracles, the blessing of Abraham and gifts.
Jesus is defining necessary characteristics of branches connected Him (the Vine); He is not talking about apostleship, or anything about the era of apostleship. What exactly is an “era of apostleship,” other than reconciling people to the truth, fellowship and Power of Jesus Christ? This is not about the era of man, but the era of Jesus. This is not about focusing on limited men; rather, it is about the limitless victory of Jesus’ atonement. This is not about being fanboys of men; rather, it is about fearing and worshiping Jesus. Regarding truth claims about reality and deductions applied to me, what do the apostles have to do with me? Do I pray to the apostles? Will the Father give me whatever I ask for in the name of James? Did the apostles themselves say, “in the name of the apostles be healed”? Did the apostles take on my curse and make me righteous? Are demons cast out in the name of “Paul”? Does Peter send the Holy Spirit? Does John give me access to the miracles that the blessing of Abraham gives me (Gal. 3:5)? Eras are identified or characterized by Jesus, not men. Jesus is still on the throne. He is still alive. With Him still, are many sons, whose life is hidden and identified with Him. He is still the righteousness of many sons today. Today, because of Him, many still have direct access to the power on High. The same Jesus who gave a Canaanite woman what she asked, even though she was outside of “God’s will” (covenant plan), is still alive and listening to those who cry out for help. Jesus still abides in people. Today, those with faith still abide in Him. He still commands discipleship, and thus, He still demands you prove your discipleship by getting exactly what you pray for.
The apostle John repeats this passage from his gospel, in his personal letter and applies it to the church at large. That is, John applies getting all the miracles, (even those greater than Jesus (14:12-12)), being defined by getting what we wish for, to the entire church. Apostleship has nothing to do with it. For man-centered men, this might upset them, but it was about Jesus. It was about faith in His Name. He is still alive. He is still in authority, and in fact, is in a greater place of authority. He is the defining factor here. He is still giving out the gift of the Spirit. He is still giving out the spoils of His triumph and plundering of the grave, sin and Satan. The curse of the law is still buried in the grave in His death, and the blessing of the law still clothes Him like a robe; furthermore, we are still identified with Him in both His death and the blessed life He lives. Our death is still buried with Him, and our life is still clothed with the blessing of the law in Him. In fact, we are given the ring, sandals and robe of sonship. We are not only robed with “the blessings of the law” in Christ for us (Deut 28), but we are clothed as heirs of God in Christ. We still have the Mind of Christ. All things are still ours in Christ. It was always about Him, not men.
“Now this is the confidence we have before Him: Whenever we ask anything according to His will, He hears us. And if we know that He hears whatever we ask, we know that we have what we have asked Him for.” 1 John 5:14-15 HCSB.
Note, “God’s Will” here, is defined as God’s commandments, and not decrees. God commands and precepts include all sorts of things such as the command to repent and be reconciled to God; but it also includes things like success, healing and prosperity. Therefore, most prayers (by born again Christians) are in fact according to “God’s Will, or his precepts”. Thus, our confidence is as John says, if we ask in line with God’s commands, we get what we ask for. Some, discovering that their experience does not resemble what John says, will become David Hume empiricist and exchange the truth of God for a lie. They will make truth based off “their” human speculation rather than “Christ’s” revelation. They are practicing atheists, and they like it. However, for believers, we will exchange the lie of our human speculation for the truth of Christ. We will blame our weak of faith, and then in the strength of Jesus Christ grow in sanctification and become victorious. We will submit ourselves to God and obey Him. And so, the issue is often faith or lack thereof, and not a misapplication of God’s Will/ commands when we pray.
 I would recommend Vincent’ essay “Miracles and Predestination,” which talks about this passage from predestination.
For further reading I would recommend Vincent Cheung’s essay, “Two Views on God’s Word.” Here he righty says such passages like this is meant to expand our options in life, and not limit them. This can be applied to others passages such as Psalm 34, 37, 91 (etc). [Again, as a reminded for clarification: I do not represent Vincent, I just like reading and recommending his stuff. I might disagree with him on occasion, or because I am not perfect, might misunderstand him.]