How do you find percentage for edible yield?

No. Edible yield will vary for every product.

For meat it varies greatly between species.

Fish tend to have less mass of bones because their bodies are supported by water. It also depends on what you are willing to eat. People in Asia will eat parts of the heads and offal of many more animals than people in the West. However, a lot of these bits end up in products where we don't know exactly what body part it came from. For fish the fillet yield for a salmon is much higher than a tilapia for example. There is no hard and fast rule to how much the edible yield is for any animal but agricultural scientists are active in improving the yields constantly.