Sayak, What you mention is there in Max Muller's translation, but I do not find it in Charles Johnston's translation or in that of Swami Nikhilananda. It is not there in Robert Hume's translation. It is not there in Swami Swahananda's translation. Perhaps I am looking at some other prapathak/khand etc. Links here:
The Thirteen Principal Upanishads and
Chandogya Upanishad (taken from Wikipedia - Chandogya Upanishad).
As for King Pariks()it in AtharvaVeda, there is nothing to show that it is the same as Srimad Bhagwat Purana's Pariks()it and grandson of Arjuna.
You got confused by the numbering system. Look at Chhandayoga Part 3 Chapter XVII of Nikhilananda (its in the famous honey doctrine section)
Chandogya Upanishad
Ghora, of the line of Angirasa, communicated this [teaching] to Krishna, the son of Devaki—and it quenched Krishna’s thirst [for any other knowledge]—and said: “When a man approaches death he should take refuge in these three [thoughts]: ‘Thou art indestructible (akshata),’ ‘Thou art unchanging (aprachyuta),’ and ‘Thou art the subde prāna.’”
How many Pariks-hit, a famous and universal sovereign of the Kaurava clan do you think there are?
The Hymns of the Atharvaveda, Book Twenty
7List to
Pariks-hit's eulogy, the sovran whom all people love,
The King who ruleth over all, excelling mortals as a God.
8'Mounting his throne, Pariks-hit, best of all, hath given us peace
and rest,'
Saith a
Kauravya to his wife as he is ordering his house.
9'Which shall I set before thee, curds, gruel of milk, or barley-
brew?'
Thus the wife asks her husband in the realm which King
Parik**** rules.
10Up as it were to heavenly light springs the ripe corn above the
cleft.
Happily thrive the people in the land where King Pariks-hit
reigns.
11Indra hath waked the bard and said, Rise, wander singing here
and there.
Praise me, the strong: each pious man will give thee riches in
return,
12Here, cows! increase and multiply, here ye, O horses, here, O
men.
Here, with a thousand rich rewards, doth Pūshan also seat him-
self.
13O Indra, let these cows be safe, their master free from injury.
Let not the hostile-hearted or the robber have control of them.
14Oft and again we glorify the hero with our hymn of praise, with
prayer, with our auspicious prayer.
Take pleasure in the songs we sing: let evil never fall on us.
