One of the most noticeable changes on the Pixel 2 is the search bar on the home screen. It has been moved to below the dock. Unfortunately, you can't change this in the default Pixel launcher. You'll need to install a 3rd-party launcher, such as Nova Launcher. If you do install a 3rd-party launcher, look in the home screen settings for persistent search bar, or just use the search bar widget and put it anywhere you want.