To prepare dressing, combine first 8 ingredients in a small bowl; stir well with a whisk.
To prepare salad, combine half of dressing mixture, grapefruit, orange, and clementine in a large bowl; toss gently to coat. Arrange grapefruit mixture in a single layer on a platter. Combine remaining dressing, watercress, and arugula in a large bowl; toss gently to coat. Top orange mixture with watercress mixture; sprinkle with toasted sliced almonds.