The bush is about 5 feet tall and 5 feet wide. It's planted in a corner of a privacy fence and can't spread out all the way around. I would like to split it so it can grow better and then plant the splits else where in the yard.
Can You Divide a Knockout Rose Bush?
Unless it has sent out suckers, it can't be divided. You can check the base of the plant to see if suckers have been produced, but this is unusual for Knockout roses.
What you can do is start new plants from cuttings. This article will help with this: