Hi MHasan,
I was also perplexed by this vague description as well. Luckily I found the solution by looking at the default installation templates.
The name of the element is the Table of Contents when in Layout mode. Adding a open and closed curly bracket will add the element to the Print Layout Template JSON's "customTextElements" array.
Below is a screen capture of the "Get Layout Templates Info" which has successfully added the "{VeryCustomElementName}" dynamic element to the print template