I'm not sure the indulgence applies to Feasts of Our Lord, but it can't hurt to recite it. If it is indulgenced, great. If not, you've honoured Christ the King!
V. O Lord, hear my prayer.
R. And let my cry come unto thee.
Let us pray.
Almighty and everlasting God, who in thy beloved Son, the King of the whole world, hast willed to restore all things: mercifully grant that all the families of nations, now kept apart by the wound of sin, may be brought under the sweet yoke of his rule.
Who with thee liveth and reigneth, in the unity of the Holy Spirit, God, world without end.
I would assume that this indulgence also attaches to the recitation of the Troparion and Kontakion of the Saint of the day in the Eastern Calendar which are in my Eastern Rite post at 00.06.