Good question! Actually, this is the first time I have encountered it in ELH; I'm happy to provide some insight into it.
You cannot place built-in quizzes on layers (both the Insert Quiz route and the Convert to Freeformroute), as the quiz functionality only works at the slide level. If you plan to build a custom quiz in the layers, such as the one I created in the attached Storyline file, you can store the Knowledge Check data in a variable, as shown in the screenshot below. In that sample project, I added the quiz question in a regular layer using text and buttons and then added conditions to check the results. Two other layers serve as the custom Correct and Incorrect layers.
Then for tracking, you can use the steps below to send the variable data to your LMS/LRS.
I am familiar with the layer built in questions as you did in the example, but the second part is still a mystery to a beginner level user like me. I have to study it first....