https://www.skillshare.com/classes/Knockouts-in-Illustrator-An-Illustrator-for-Lunch%E2%84%A2-Class-Making-holes-in-objects-the-smart-way/2061238639

In this course you will learn a range of techniques for making holes in one and multiple objects in Illustrator. You’ll learn tools and settings for creating transparent knockout effects which are fully editable and which use smart design skills. Along the way you will learn to use some important features of the Appearance panel and how to layer knockout effects so they impact other shapes. Each of the six techniques share similar concepts and build to give you a solid grounding in creating knockouts in Illustrator.

And it wouldn’t be an Illustrator for Lunch™ class if you didn’t also learn other Illustrator skills and techniques in the class that you can use every day.