You can see a list of all design screens in the Project manager. To quickly view each one, just select it and press the SPACE key to preview.
Click on the artboard name in the breadcrumbs in the top left corner.
You’ll see a list of all artboards in this file (in case of Sketch they will be grouped by a Page) and all symbols.
Click on any artboard or symbol to open it.
You can also type in a name of any artboard to search for it.