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1
Make broth: Simmer pork ribs, chicken, scallions, ginger, and water in a 6- to 8-quart tall narrow stockpot, uncovered, until meat is very tender and falling apart, 4 1/2 to 5 hours.
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2
Pour broth through a sieve into a large bowl and discard solids. Cool broth, uncovered, then chill, covered, at least 1 1/2 hours.
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3
Make wontons: Stir together pork, yolk, scallions, ginger, soy sauce, vinegar, sesame oil, salt, and white pepper in a bowl in 1 direction with your hand until just combined (do not overwork, or filling will be tough).
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4
Put 1 wonton wrapper on a work surface (keep remaining wrappers covered with plastic wrap). Spoon a rounded teaspoon of filling in center of square, then brush water around edges.
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5
Lift 2 opposite corners together to form a triangle and enclose filling, pressing edges firmly around mound of filling to eliminate air pockets and seal.
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6
Moisten opposite corners of long side. Curl moistened corners toward each other, overlapping one on top of the other, and carefully press corners together to seal.
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7
Make more wontons in same manner.
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8
Finish soup: Skim any fat from broth, then bring to a simmer in a 5- to 6-quart pot.
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9
Stir in bok choy, salt, and white pepper and simmer, uncovered, until bok choy is crisp-tender, 3 to 4 minutes.
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10
Add wontons and simmer, uncovered, gently stirring, until filling is just cooked through, about 3 minutes (cut 1 open to check).
