Heat oil over medium heat in a soup pot. Add onions and cook until softened, about 7 minutes. Add celery seeds and caraway seeds and cook until fragrant, about 1 minute. Add farro, potatoes, carrots and water or stock. (If using uncooked sausage, add at this time.) Bring to a gentle boil and cook 30 minutes. If liquid appears low, add additional water or stock.
If using pre-cooked sausage, add it now along with shredded cabbage and cook until sausage is heated through and cabbage has softened, about 10 minutes.