Pour chicken broth and water into a medium-size pot; bring to a boil over high heat. Lower heat to medium and add kale. Cook for 30 minutes and drain well after cooking. Meanwhile, sauté sweet potatoes over medium high heat in 2 tablespoons olive oil for 10 minutes or until almost fork tender. Remove from pan and set aside. Saute onion and garlic in the remaining 2 tablespoons olive oil over medium low heat for 5 minutes or until the onion is transparent. Stir sweet potatoes and kale gently into the onion mixture. Pour soy sauce over kale mixture; sprinkle with smoked paprika and salt. Stir to combine. Cook for 5-8 minutes. Serve warm.