add items into specific location for adjacent cells based on helper columns for two sheets

Sht1 rows 6-8 replacement data is not available?

Sub J3v16()
Dim Data, ws As Worksheet, i As Long
For Each ws In Sheets
    With ws.Cells(1).CurrentRegion
        Data = .Value
        For i = 2 To UBound(Data)
            If .Parent.Range("J" & i) > 0 Then
                Data(i, 2) = Application.Substitute(Data(i, 2), " ", " " & .Parent.Range("I" & i) & " " & .Parent.Range("J" & i).Value)
            Else
                Data(i, 2) = .Parent.Range("I" & i) & " " & Data(i, 2)
            End If
        Next i
        .Value = Data
    End With
Next ws
End Sub

My bad...see amended code...References correct sheet...

.Parent.

Run and check...

& , .Parent.Range("J" & i).Value)

Start learning not to run macro twice...Or use helper cell...

Sub J3v16()
Dim Data, ws As Worksheet, i As Long
For Each ws In Sheets
    If ws.Range("D1") = "" Then
        With ws.Cells(1).CurrentRegion
            Data = .Value
            For i = 2 To UBound(Data)
                If .Parent.Range("J" & i) > 0 Then
                    Data(i, 2) = Application.Substitute(Data(i, 2), " ", " " & .Parent.Range("I" & i) & " ", .Parent.Range("J" & i).Value)
                Else
                    Data(i, 2) = .Parent.Range("I" & i) & " " & Data(i, 2)
                End If
            Next i
            .Value = Data
        End With
        ws.Range("D1") = "X"
    End If
Next ws
End Sub

Glad to have helped...Tx for rep +