I'm fond of using User Defined Functions for things like this, but some of the worksheet formula experts might have a non-VBA way
Option Explicit
'Usage: =POandSKU(F11,$F:$F,$J:$J)
Function POandSKU(SKU As String, RangeSKU As Range, RangePO As Range) As String
Dim s As String
Dim r As Range
For Each r In Intersect(RangeSKU.Columns(1), RangeSKU.Parent.UsedRange).Cells
If r.Value = SKU Then
s = s & Intersect(r.EntireRow, RangePO.Columns(1)).Value & ", "
End If
Next
If Len(s) > 0 Then s = Left(s, Len(s) - 2)
POandSKU = s
End Function
Paul