Gawain's expected 'answer' to the "riddle", in The High Book of the Grail, is the most consciously set up of all the versions of the Grail legend. He is reminded, once he sets out on the quest, that he must be alert enough in the Castle of the Fisher King to inquire after the Grail, and thus lift the curse from the Fisher King and heal the land. In an early incident, Gawain is warned by a Damsel:

Sir Gawain turned away , and then suddenly the maiden on foot cried out:
"Sire! Sire! You are not as alert as I thought!"
Sir Gawain, startled, turned his horse back.
"Why do you say that, damsel?"
"Because," she said, "you did not ask my lady of the Cart why she carries her arm hung from her neck in that golden sling, with the rich cushion on which her arm rests. Will you be as alert at the court of the Fisher King?"
"O my sweet friend," said the maiden of the Cart, "do not hold Gawain alone guilty, but King Arthur before him, and all the knights of his court, for none had the presence of mind to ask." (40)
However, when Gawain actually gets to the Castle of the Fisher King and is presented with the marvellous sights of the Grail and the lance with the bleeding tip, he is in such awe that he is unable to speak:
Just then, two maidens appeared from a chapel: in her hands one was carrying the Holy Grail, and the other held the lance with the bleeding head. Side by side they came into the hall where the knights and Sir Gawain were eating. So sweet and holy a fragrance came froth that their feasting was forgotten. Sir Gawain gazed at the Grail and thought he saw therein a chalice, which at that time was a rare sight indeed; and he thought he could see two angels bearing two golden candlesticks with candles burning. The maidens passed before Sir Gawain and into another chapel. Sir Gawain was deep in thought, so deep in joyful thought that he could think only of God. The knights stared at him, all downcast and greiving in their hearts. But just then the two maidens came out of the chapel and passed once more before Sir Gawain. And he thought he saw three angels where before he had seen but two, and there in the centre of the Grail he thought he could see the shape of a chid. The foremost knight cried out to Sir Gawain, but he looking before him, saw three drops of blood drip on the table, and was so captivated by the sight that he did not say a word. And so the maidens passed on by, leaving the knights looking at one another in dismay. Sir Gawain could not take his eyes off the three drops of blood, but when he tried to kiss them they moved away from him, and it grieved him deeply that he could not touch them with his hand or anything within his reach. Thereupon the two maidens passed once more before the table, and to Sir Gawain, it seemed that there were three; and looking up it appeared to him that the Grail was high in the air. And above it he saw, he thought, a crowned king nailed to a cross with a spear thrust in his side. Sir Gawain was filled with sorrow at the sight and he could think of nothing save the pain that the king was suffering. Again the foremost knight cried out to him to speak, saying that if he delayed longer, the chance would be lost forever. But Sir Gawain remained gazing upwards in silence, hearing nothing that the knight had said. The maidens disappeared into the chapel with the Grail and the lance, the knights cleared the tables, left the feast and moved off into another chamber, and Sir Gawain was left alone. (80)
Selections from The High Book of the Grail. Translated by Nigel Bryant.