To make the cake: Preheat the oven to 350 degrees F. Lightly oil an 8-inch-diameter cake pan. Whisk the flour, baking powder, and salt in a medium bowl to blend. Using an electric mixer, beat the sugar, eggs, and zests in a large bowl until pale and fluffy. Beat in the milk. Gradually beat in the oil. Add the flour mixture and stir just until blended. Stir in the almonds. Transfer the batter to the prepared pan. Place cake pan on baking pan to collect any possible spills. Bake until a tester inserted into the center of the cake comes out with moist crumbs attached, about 35 minutes. Transfer to a rack and cool for 15 minutes. Remove cake and place on serving platter, top side up. Sift powdered sugar over the cake.
To make the citrus compote: Stir the orange peel, blossom water, and 2 tablespoons of accumulated juices from the segmented fruit in a small bowl to blend. Arrange the orange and grapefruit segments decoratively in a wide shallow bowl. Pour the blossom water mixture over. Cover and let stand 15 minutes for the flavors to blend.
Cut the cake into wedges and spoon the citrus compote alongside.