How can I refer to a field on a portal?

Classic Servoy
1

How can I refer to a field on a portal?

I have tried:

forms.formname.portalname.fieldname

and

forms.formname.elements.portalname.fieldname

and

elements.portalname.fieldname

and

portalname.fieldname
2

That’s simple.

relation_to_relation.fieldname
3

Thank you !!!