This is a activity challenge for Apple Watch that Apple specifically focuses on Veterans in the United States. It is not a date that is celebrated throughout the world and that is why it is basically for the North American country.
This challenge has been going on for a long time and it is about perform any type of training of 11 minutes or more on Monday, November 11, which is Veterans Day. Without a doubt, it is a good way to encourage the movement of the challenges of the Apple Watch and in this case it is not very physically demanding so everyone can try to get the medal.
All users who have an Apple Watch and who reside in the United States can carry out this activity in which they get the stickers to use in the Messages application and the medals for the Activity app. In this case they are same as the ones they gave last year in terms of design. The activity will be visible from next November 9 and on the 11th will be the date on which the challenge can be achieved.
Regarding the activity challenges for the rest of the Apple Watch users, no new ones are expected (at least for now) for this year and the rest of the National Parks took place on August 25 and that was the last. Now for the beginning of 2020 it is expected that the "Start the year on the right foot" that we will see possibly in the month of January, until then it does not seem that we will have any more challenges.