To select cell D4 on a worksheet (Sheet2) in a different workbook (Book2.xlsx), you can use either of the following examples:
Application.Goto Workbooks("Book2.xlsx").Sheets("Sheet2").Cells(4, 4)
-or-
Application.Goto Workbooks("Book2.xlsx").Sheets("Sheet2").Range("D4")
You can also activate the worksheet, and then use method 1 above to select the cell:
Workbooks("Book2.xlsx").Sheets("Sheet2").Activate
ActiveSheet.Cells(4, 4).Select
ActiveSheet.Cells(4, 4).Select