Great question!

At this time, we are only able to pull in object attributes that are associated with profiles. So in order to reference an Object’s attributes, your customer would need to be associated with that Object either via the workflow action or our API (as you mentioned, knowing the identifier of both the customer and the object are necessary to make this relationship).

Once you have associated the object with the customer’s profile, this part of our documentation discusses how object attributes can be referenced with Liquid: https://customer.io/docs/journeys/objects/#use-objects-in-liquid

NOTE: In the future, we plan to add methods for defining the object(s) you want to reference in liquid instead of being limited to the 10 most recently added per type.

Hi! I was wondering the same question. I would like to use object data in a campaign where the person is not yet related to the object.
Would be great to have this feature in the future.

You could try using collections, but my guess is that those won’t work for what you’re thinking of building. Those are used more for something like events.