There are, as you know, some pieces of information in the world that you know are out there, but which you know to be a secret. Some are very important, say, the nuclear launch codes. Others are... rather less so, such as who Carly Simon wrote 'You're So Vain' about.
Another one of those secrets is the identity of KFC's 11 herbs and spices. The thing is, though, the answer to that particular secret is right in front of you every time you buy the chicken. The herbs and spices have been given to you, just mixed up. You can taste them and everything. And if you can taste them, you can start to sort them out. One of Hell's Kitchen's recurring challenges is called 'Taste It, Then Make It': Gordon Ramsay gives you a dish, and your task is to figure out the ingredients and recreate it. A related challenge gives you a dish with a large number of ingredients, and you're asked to list the ingredients. There's no reason that can't be done here as well. KFC, however, has every incentive not to give it up. After all, it's a valuable trade secret. If it gets out, there's nothing to stop any and all competitors from making their own variations and cutting into KFC's business. In fact, when KFC gets outside contractors to make the seasoning, they use at least two different companies and gives each only half the recipe so that neither knows all of it.
However, one man, a few years ago, is considered to have successfully reverse-engineered the recipe. Ron Douglas of Glen Cove, New York, in 2009, first tried to weedle it out of the KFC employees. They, however, don't know it themselves; the seasoning comes prepackaged. So then he set out to make it himself. He admits that he wasn't able to make an exact match, and that doing so is likely impossible without a pressure fryer that KFC has and you don't. However, he thinks he has the recipe.
That's the good news. The bad news is that Douglas considers the key spice, out of the 11, to be Accent. You know that better as MSG. The other 10 spices, as per his figuring: chili powder, dried basil, dried marjoram, garlic powder, ground oregano, ground sage, onion salt, paprika, pepper and salt. He figures two tablespoons of Accent and salt; everything else is one tablespoon. The Guardian went and crowdsourced a non-MSG recipe; that can be seen in the link in this paragraph.
There is no real way to know for sure whether this recipe is correct, and KFC sure isn't talking. But it would be one more reason the 11 herbs and spices are secret: one of them is embarrassing.