PCB holes are essentially drill holes. To view PCB holes, import all gerber files and Drill data (or import other PCB formats which already have drill embedded like: ODB++, IPC-2581).
Here's a screen capture how PCB holes (i.e drill holes) are displayed in the editor:
Note: By default, PCB holes are displayed as clear with a cross. To change the display of drill holes to SOLID (similar to many other editors), please view the following link:
If you do not have any Drill files (i.e Gerber files only), you can create a Drill layer from those gerber files. Please view the following link,