Nested Expression: Using dynamic field when referencing Value from an action flows

I've posted this twice in the Power Automate forum but havn't received a response. So I'm posting here to see if anyone might have some insight. 

Lets say you have an action We will call it action A with fields 1,2,3.  Then we have List B. each record of the list contains two values ASchemaField, and AfieldValue.

you will need to loop through List B records until you can match ListB.AfieldValue  with its appropriate Action A field.

How would you go about resolving this Expression to reference the correct action A field?  My method seems to always return blank. Below are a few iterations I have tried to return.

outputs('action_A')?[items('Apply_to_each')?['List_B.ASchemafield']]

outputs('action_A')?[concat('''','body/',items('Apply_to_each')?['List_B.ASchemafield'],'''')]

outputs('action_A')?[concat('''',items('Apply_to_each')?['List_B.ASchemafield'],'''')]

My other post is referenced here and is more specific to my scenario https://powerusers.microsoft.com/t5/Using-Flows/Inception-Expression/m-p/1616907#M31250