Hi,
Probably depends on the reasons to separate data in different modules/applications in the first place. I'll call the first application A (that consumes data) and the second application B (that produces data), and I'll call modules End-User A/B and Core A/B accordingly.
Does the Core A need the data from the Core B? If not, why implement an extra Action in Core A that just acts as an indirection to Core B and add the extra dependency?
Would there be safeguards as to who/when data from Core B can be accessed? if so, then you may want to consider an Action on Core B, but you could probably call it directly from End-User A.
In general, for reads, you're probably better off using an Aggregate directly from End-User A that fetches data made Public (but most likely Expose Read-Only) in Core B. This will allow for extra optimisation by the platform when called from the Preparation, for instance.