In a 1- to 1 1/2-quart pan, mix 1/4 cup sugar and the gelatin. Stir in 1/3 cup cold water; let stand until gelatin is soft, about 5 minutes. Stir over medium-high heat until gelatin and sugar are dissolved, about 2 minutes. Stir in milk and almond extract. Pour into 9-inch square baking dish or pan. Chill until firm, at least 3 hours; cover if storing longer (see notes).
With a vegetable peeler, pare six thin 4- by 1/2-inch strips of peel from orange. Ream juice from orange and reserve. With the flat bottom of a glass, crush cardamom pods; remove and discard hulls. Place orange peel strips, black cardamom seeds, and remaining 1/2 cup sugar in a 1 1/2- to 2-quart pan. With a wooden spoon, crush peel and seeds with sugar. Add 4 cups water; stir over high heat until sugar is dissolved, about 1 minute. Let cool, then add reserved orange juice; cover and chill until cold, at least 1 1/2 hours. Pour through a fine strainer set over a large bowl.
Cut almond gelatin into 3/4-inch squares; also run knife around pan sides. With a wide spatula, carefully lift out cubes and add to orange-cardamom syrup. Add raspberries and mandarin oranges with their syrup; gently mix to distribute fruit evenly. Serve or cover and chill until ready to serve (see notes). Ladle into small bowls or glasses.