To determine the correct equation Gwen can use to find \( x \), the normal cost of an individual, let's break down the problem.
The total cost for 14 people with the group package is $504. Given that this cost is $6 less per person than the normal cost for an individual, we can express the cost per person for the group package as \( x - 6 \), where \( x \) is the normal cost per person.
Since they are buying a package for 14 people, the total cost for the group can be expressed as: \[ 14 \times (x - 6) \]
Setting this equal to the total group package cost of $504 gives us the equation: \[ 14(x - 6) = 504 \]
Therefore, the correct choice is: \[ \boxed{14(x - 6) = 504} \]