If the rows in that second portal are in sync with those of the first one, then you can (probably) simply put the field from the second portal into the first. (“Probably” because we don't know anything about your data model, relationships etc.)
A portal can only show records from one table, but it can display fields from any other related table occurrence. It is up to you to define your data model so that the relationship/field returns sensible data in the portal context.
Class --< Enrolment >-- Student
a portal on a Class layout can show records from Enrolment, but only contain a name field from Student, since every Enrolment records knows “its” related Student record. (This also works the other way around to show Class names on a Student layout.)
So that usually negates any need to put portals on top of each other.
V. useful insight.....and yes, because these fields are from related tables, bringing fields from a different portal appears to work in synch.
Yes, as pointed out by erolst, you can use within a portal, fields from any other TO on that same relationships chain. This will be a much more robust approach than trying to overlay separate portals.