You can find statistics about a skill by going to the skill's page. At the top of the page you'll find the statistics of the skill:
This is the average rating of all the bookings for the skill.
This is the total number of hours booked for the skill.
This is the total number of unique customers for the skill.
Don't confuse these statistics with the ones shown on an instructor's page. The statistics shown on an instructor's page are for that instructor in particular.
If you want to learn more about an instructor's statistics, then please read this article.