See T341142 for details. The column will initially have a default value, which will be removed next week (I will create another schema change task for that).

ALTERs to run:

ALTER TABLE campaign_events ADD COLUMN event_answers_status INT DEFAULT 0 NOT NULL;

1. Where to run those changes: These tables are all in the extension1 cluster. In particular, they can be found in the per-wiki databases of testwiki, test2wiki, and officewiki, as well as in the wikishared database. So it's a total of 4 places.
2. When to run those changes: Whenever you can (ideally before next week's train)
3. If the schema change is backwards compatible: Yes (the new column has a default value)
4. If the schema change has been tested already on some of the test/beta wikis: Tested locally and in beta
5. if the data should be made available on the labs replicas and/or dumps: Maybe, but we don't replicate data from x1 anyway.