In James 1:5 we read, "If any of you lacks wisdom, let him ask of God, who gives to all men generously and without reproach, and it will be given to him." Mormons often appeal to this verse in asking people to pray about the Book of Mormon to see if it's true.
The Mormon interpretation jerks this verse out of its context. The meaning of James 1:5 is connected to the preceding verses which speak about the purpose of trials (verses 2-4). James anticipates that some of his readers will say they cannot discover any divine purpose in their trials. In that case, they are to ask God for wisdom.
Furthermore, even if James is not referring to gaining wisdom about the purpose of trials but is rather talking about wisdom in general, God's "wisdom" on a matter never contradicts what He has recorded in Scripture. For this reason, one need not pray about matters that God has already given us His verdict on. One does not need to pray about whether to worship another god because the true God has already said it is wrong (Exodus 20:3). One does not need to pray about whether to participate in spiritism because God has already said it is wrong (Deuteronomy 18:9f.). Likewise, we need not pray about the Book of Mormon because God has already condemned all gospels that contradict that found in the Bible (Galatians 1:6-8).
Finally, it should be stressed that prayer is not the test for religious truth. We are instructed by the apostle Paul in 1 Thessalonians 5:21 to objectively "test all things," not pray to receive a subjective feeling that something is true. Though the Bereans believed in prayer, their barometer for truth was not prayer but Scripture (Acts 17:10-12). We should follow their example.
