Bump In Middle Of Tummy

My yorkie is 10 weeks old and she has a small raised knot below her ribcage in the center. I guess that's her navel? It looks strange to me.

There are two structures that could fit your description.  Her navel is one possibility and just like people there are many features that a navel could have and be normal.  Some are barely perceptible and others are firm, raised or rough.  Umbilical hernias are common in puppies in which case there is a small amount of fat that protrudes through the opening in the abdominal wall. These are usually soft and you can often push the fat back through the opening without discomfort to you puppy.

The second structure is the xiphoid cartilage which is a firm knot under the skin tucked up in the "V" of the rib cage.