I've used the story Lazarus and the rich man (Luke 16:19-31) to show consciousness between death and resurrection, but Jehovah's Witnesses argue that it is just a parable and thus does not tell us anything about the real world. How can I respond to this?
Point out that Jesus' parables tell us much about the real world. He takes common elements of human experience--sons and fathers, judges and kings, the rich and the poor, buying and selling, planting and harvesting, fishing and wine-making--and uses these elements to teach theological points.
In the parable of Lazarus and the rich man Jesus uses human experiences of life and human experiences of death to teach that one's life affects one's fate, that one's fate is sealed at death, and that those who will not listen to God's word will not take heed of his own Resurrection either.
Point out that if his other parables reflect human experience when they talk about comfort and suffering in this life then this parable reflects human experience when it talks about comfort and suffering in the afterlife between death and resurrection.
To press the issue more sharply, point out that the second half of the parable (where the two are dead) reflects human experience as much as the first half (where the two are alive) reflects human experience. If there were rich men and beggars in Jerusalem in Jesus' day, then, when they died, they went to hell or Abraham's bosom in Jesus' day.
They went to hell if unrighteous (the Catechism of the Catholic Church, following the historic Christian interpretation, cites the rich man as an example of one who has died in mortal sin [CCC 1859]) or to Abraham's bosom if righteous (today the state of the righteous dead is even more glorious since the gates of heaven have been opened and the righteous, after purification if needed, now go to be with God (CCC 1026).
Note that some argue this isn't a parable at all but a historical account. Nothing in the text says it is a parable, and it is different from other parables in that Jesus names one of the characters--Lazarus. If it is a parable, it is the only parable where that happens.
A few last points. When the rich man suggests Lazarus be sent back from the dead, Abraham does not say that he won't go back, but that if he does go back those who will not hear the Law and the prophets will not take heed of Lazarus's rising either. In John's Gospel we read that Jesus has a friend named Lazarus who dies and comes back from the dead (Jn 11), and when he does so those who do not listen to God's word do not heed his raising either (Jn 11:45-53); they even plan to kill Lazarus because of the evidence his raising provides for Jesus' messianic claims (Jn 12:9-11)!