I want to add fields from Table - "Customer Bank Account" in Page - "Bank Receipt Journal" which has a current source table as "Gen. Journal Line".
It might be helpful if I get to the know the process for adding fields as a lookup from different Table source.
I guess it depends on your requirements:
If you think the additional fields may also be used on other pages that have "Gen. Journal Line" as their SourceTable, I would consider adding FlowFields of method "Lookup" to your "Gen. Journal Line" table (assuming you have sufficient permissions to do so). In your response, please elaborate on how you want your lookup logic to work for further assistance, if needed.
If your lookup logic is more complex than FlowFields can handle, a function on the "Gen. Journal Line." that returns the relevant field value may be a good solution.
Alternatively, if this is the only page where you will need your new fields, or if you don't have permissions to modify table definitions, define a function in your page object that performs the lookup and returns the value. Use this function as the SourceExpr of your page control.