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The owner of Job and Dust & Ashes can choose to "instead" Stalks of Flax, because it is harm. Harm is "any effect from cards not of the same alignment (i.e., good, evil, or neutral) targeting a character", and Stalks of Flax is a different alignment than Job.
anyways... where does an exchanged job go if there are 2 dust and ashes out and he is harmed