Here's one way:
Sub Checker()
Dim dataRange As Variant
Dim StoreData
Dim dataOut() As String
Dim counter As Long
' Define the range starting from B2 to the last cell with data in column B
With Range("B2:B" & Cells(Rows.Count, "B").End(xlUp).Row)
dataRange = .Value
StoreData = .Offset(, -1).Value
ReDim dataOut(1 To UBound(StoreData, 1))
End With
' Iterate through the array
Dim idx As Long
For idx = LBound(dataRange, 1) To UBound(dataRange, 1)
If dataRange(idx, 1) = 0 Then
' If the data value in the cell is 0, add the value of the cell to the left to the array
counter = counter + 1
dataOut(counter) = StoreData(idx, 1)
End If
Next idx
' Check the array
If counter = 0 Then
' If the array is empty, show a message box
MsgBox "No store data is missing."
Else
' If the array has data, construct the missingData string
ReDim Preserve dataOut(1 To counter)
missingData = Join(dataOut, ",")
' Show a message box with missing data
MsgBox "Data missing from: " & missingData
End If
End Sub