Simmer liver and chicken broth in a medium saucepan, covered, until liver is no longer pink in center, 5 to 6 minutes.
With a slotted spoon, transfer liver to a food processor. Add 1/2 cup cooking liquid and whirl until smooth. Add 1/2 cup more liquid, wheat germ, and 1 1/2 cups flour; pulse dough until evenly moistened.
Preheat oven to 325°. Turn out dough onto a lightly floured work surface and knead a few times until smooth, adding a little more cooking liquid if needed. (Dough should be dense but moist, with no dry patches.)
Lightly re-flour work surface and using an unfloured rolling pin, roll out dough 1/2 in. thick for large or medium biscuits, or 1/4 in. thick for small ones. Cut with heart- or bone-shaped cutters (5 to 7 in. for large treats, 3 to 4 in. for medium, or 1 to 2 in. for small). Reroll scraps, adding a little more liquid if needed. Discard remaining liquid.
Transfer cut dough to 2 or 3 baking sheets lined with parchment. With a wooden skewer, deeply carve your dog’s initials or name.
Bake until well-browned on underside and spring back in center when pressed, 25 to 40 minutes for large or medium biscuits, 15 to 20 minutes for small ones. Loosen from pan with a wide spatula. Turn off oven and leave treats until hard, 3 to 4 hours. Chill airtight up to 2 weeks or freeze up to 3 months.
Makes 14 large, 16 medium, or 120 small biscuits