Pass from a for cicle to a search cicle

Try:

Sub foo()
Dim rng1 As Range, rng2 As Range, c As Range

Set rng1 = Sheet1.Range("A1:A322000")
Set rng2 = Sheet1.Range("J1:J234100")

Application.ScreenUpdating = False

For Each c In rng1
    If Not c.Value = "" Then
        If Not rng2.Find(c.Value, lookat:=xlWhole) Is Nothing Then c.Offset(0, 2).Value = "X"
    End If
Next c

Application.ScreenUpdating = True

End Sub