Communication, meaning the ability to exchange ideas, not just trumpet your own.
Attractive: People love other people who listen to them and provide thoughtful feedback.
Valuable: Communication is basically all that managers, salespeople, politicians, and consultants do. You can make enormous amounts of money without having any concrete technical skills. I have a friend who talked his way to being the head of digital at a massive corporation (moving up through social media ranks). He's 29 and has absolutely no skills other than talking.
Learnable: People will dispute this, but with concerted work and a willingness to go (way) out of your comfort zone, you can learn to communicate. For a lot of people, it isn't worth it. It's scary, embarrassing, anxiety-inducing, and all other manner of unpleasant. That's what continues to make it a valuable skill on its own.