When it comes to the knot for the Whopper Plopper, there are a few options that you can consider. In the video context provided, the anglers don't specifically mention the knot they use for the Whopper Plopper, but they do mention using braid and fluorocarbon lines.
For braid, a popular knot choice is the Palomar knot. It's a simple and strong knot that works well with braided lines. To tie the Palomar knot, you would double the line and pass the loop through the eye of the hook. Then, tie an overhand knot with the loop and pass the hook through the loop. Finally, tighten the knot by pulling both ends of the line.
If you're using fluorocarbon line, another option is the Improved Clinch knot. This knot is reliable and easy to tie. To tie the Improved Clinch knot, you would pass the line through the eye of the hook, then make 5-7 wraps around the standing line. After that, pass the tag end of the line through the small loop formed above the eye of the hook. Finally, moisten the knot and tighten it by pulling the tag end and the standing line in opposite directions.
It's important to note that the choice of knot may also depend on personal preference and the specific fishing situation. Some anglers may have their own preferred knots for the Whopper Plopper based on their experience and the type of line they are using. If you're unsure, it's always a good idea to experiment with different knots and see which one works best for you.