I am using a pre-built template dashboard and am trying to see the data that the chart widget is referencing which is displaying on the dashboard but am unable to determine what data is being used.
If you click on the Edit button in the top left corner of the dashboard, you will be able to edit the widgets.
Hovering over a widget then clicking on the small pencil icon in the top right corner will allow you to edit the widget.
For chart widgets, clicking on the Edit Data button in the Chart & Data section (shown in the screenshot) will bring up a list of all sheets and reports that you have access to for use in a chart widget (this will be on the left of the dialog box that pops up). The sheet or report with the blue checkmark next to it is the one currently being used. GENERALLY speaking, if a sheet or report is already being used, the list of sheets and reports available for use will start with the sheet or report being used somewhere close to the middle of the displayed list as soon as the dialog box opens.