Thank you for helping!
Here is the code I tried. I must be referencing incorrectly. On a Project opject report
EXISTS:A:$$OBJCODE=PROJ
EXISTS:A:ID=FIELD:projectID
EXISTS:A:expense:DE:Expense AOR TA Flag=1
or
EXISTS:A:$$OBJCODE=PROJ
EXISTS:A:ID=FIELD:projectID
EXISTS:A:expense:Expense AOR TA Flag=1
or on an Expense object Report
EXISTS:A:$$OBJCODE=PROJ
EXISTS:A:ID=FIELD:projectID
EXISTS:A:expense:Expense AOR TA Flag=1
or
EXISTS:A:$$OBJCODE=PROJ
EXISTS:A:ID=FIELD:projectID
EXISTS:A:Expense AOR TA Flag=1