The "Knight's Tale" is a romance, a fairy tale, a quest of and for the ideal. Its exemplum deals with the ideal forms of love and chivalry. As such, its major symbols have to do with the quest: knights, goddesses, the battlefield, the hand of the beloved, the test of combat, the meeting by the trees, the choice of the beloved.
Here are some other symbols/motifs/and imagery, with quotes as support:
Seasons: "morn in May"; "talk of green, And fresher than is May with flowers new"
Nature: "That “Fields have eyes and every wood has ears. It’s well for one to bear himself with poise;"
Prison: prisoner, As was his wont, by leave of his jailer"
Gods/mortals: "Whether she is a woman or goddess! Yours is a worship as of holiness, While mine is love, as of a mortal maid;"
Heaven/Hell: "No more in Purgatory, but in Hell."..."In prison? Never, but in Paradise!"
Fate vs. choice: "Of what great God, or Fortune, may ordain, When better is the gift, in any guise,"