If it is a slow cooker (SC) you are using, you can start your stock in it on high. Then lower it when the chicken is done.
To start from scratch, simmer your chicken parts until tender in your slow cooker. You can also put your veggies in the stock about 45 minutes before do the dumplings. Remove the chicken and pick off the meat.
Keep in mind, that it is going to take longer making it in a slow cooker. What you are basically making is a chicken soup with dumplings. Only you are making it in the SC than on top of the stove.
Should you want to thicken slightly, make the roux in a separate pan on top of your stove. Add about two cups of the stock slowly, stirring constantly, then add it back into your SC.
Keep in mind that when your chicken is simmering, it will release some on its own juices. So only add enough water at the beginning so that when the chicken and veggies release their juices, there won't be too much stock. Then you will have an overflow and a somewhat weakened flavored stock.
OR! Do you have available to you, chicken stock on the shelves of your grocery store? You can use that for the start of your stock. But then again, remember the chicken and veggies will add their own juices, giving you a very intense flavor for your stock.