Lightly beat the egg white in a large bowl. Add the shrimp, jicama, scallions, cornstarch, rice wine, sesame oil, 3/4 teaspoon salt, the sugar and pepper. Stir well until the mixture starts to thicken, about 1 minute; cover and refrigerate until very cold, about 1 hour.
Set 1 dumpling wrapper on a clean surface (keep the rest covered with a damp paper towel so they don't dry out). Stir the shrimp mixture, then scoop 1 heaping teaspoonful onto the center of the wrapper. Dab a finger in a cup of cold water and moisten the edges of the wrapper. Fold in half and press the edges together to seal; transfer to a baking sheet. Cover with a damp paper towel while you form the remaining dumplings.
Fill a large nonstick skillet with 1/4 inch of water and bring to a boil. Working in batches, add the dumplings and arrange in a single layer, cover and let steam until cooked through, about 5 minutes. (If the water evaporates before the dumplings are fully cooked, add 2 more tablespoons to the skillet.) Carefully transfer the dumplings to a serving plate.
Ponzu Dipping Sauce
Combine 3 tablespoons ponzu sauce, 1 teaspoon soy sauce, 1/2 teaspoon sesame oil and 1 chopped scallion in a small bowl.