You can create hole features in assemblies.
To create an assembly feature hole:
-
Click the planar face approximately where you want to create the hole.
-
Click Simple Hole
or Hole Wizard 
(Features toolbar), or click , then Simple or Wizard.
-
Set the options as needed in the Hole PropertyManager or Hole Wizard
Type PropertyManager. Under Feature
Scope, specify which components you want the feature to
affect.
You can use
Hole Series to create an assembly feature which creates hole features in the components of the assembly.
Some designers create holes using assembly features when they really should be creating hole features in the individual parts. For these designers, the SOLIDWORKS application has the Hole Series tool. This tool creates assembly feature holes, but the hole geometry is created in the individual part documents, not in the assembly.