Hi
When recording workouts via the Workout app, choose the activity type that most closely matches your workout. This enables your watch to use the most appropriate sensors and data sources when estimating results, including using tailored calorie calculations for some activities.
To record skating workouts - along with other activities that are not included within the main list or that are not sufficiently similar - record your workout under "Other".
This credits one minute of Exercise for each full minute of the workout and Active calories at a rate equivalent to a brisk walk or based on data from the heart rate sensor, whichever is higher. (Note that a route map will not be recorded for Other workouts).
To record your workout as "Skating": when ending your workout in the app, tap on the menu option for "Name Workout" and select "Skating" from the list of activities.
More information:
Work out with your Apple Watch - Apple Support