You will receive this quest while talking with Zoltan and Saskia in the tunnels for the Hatred Symbolized and Blood Curse quests. You will have to set out and find the spear used by Iorveth, which he lost in a dice game. Although this quest sounds extremely difficult, it is actually pretty easy if you know how to approach it. You will have to find Skalen, as he was the one who won the spear in a game of dice. Being a betting man, Skalen will ask that you play him in dice for the spear. Exit the tunnels from the same entrance that you came in from, and then head to Vergen’s gates to find Skalen. Sure enough, he will ask you to play him in a game of dice.
Agree to play him. Dice in The Witcher 2 basically just boils down to luck, so keep repeating the games even if you lose a lot to win the spear eventually. Skalen will offer to play you a few more times. You should accept this offer. It won’t get you any story-essential items, but it will give you enough to help out with the Death Symbolized quest later on, as well as some other decent winnings. When you have the spear in hand, return to the tunnels. Head through them the same way you did before to find Zoltan and Saskia in the upper corner of the tunnels. Speak with them to inform them of your success. You will have completed the Spear of Destiny quest, and you will be ready to tackle the next leg of the Blood Curse quest.