I am trying to set a source worksheet variable to a target worksheet variable in another workbook(DataSource1.xlsx) with the purpose of eventually using it to read the target wo
If the workbook is already opened, you need to refer to it by name without path:
Set source = Workbooks("DataSource1.xlsx").Sheets("Sheet1")
If the workbook is not opened yet, you need to open it first:
Set source = Workbooks.Open(ThisWorkbook.path & "\DataSource1.xlsx").Sheets("Sheet1")