In design view, the report property sheet data tab will expose its recordsource. The expression you posted shows that control is a calculated one, not bound to the underlying source. RegEWaiverAmt(Day) is a poor name for a control or field in that it uses special characters and what looks like a reserved name (Day) - unless the whole thing is a function call with a parameter. I suspect the control regarding your post is only performing an aggregate function (e.g. Sum) on some other control or field named RegEWaiverAmt(Day) in the report. If looking at the report recordsource does not answer your question (i.e. there is none), there must be a form that opens this report and sets the report source in that event.
There is no module in this database
AFAIK, every form or report has a module behind it whether you use it or not. Try opening the vb and look for code in the report module or form module if there is one.
What I mean about poor names...http://allenbrowne.com/AppIssueBadWord.html#D
The more we hear silence, the more we begin to think about our value in this universe.
Paraphrase of Professor Brian Cox.