Nothing happens. Zn metal can't donate electrons to zn2+ ions (because they're the same species).
Zn metal you could say is made up of zn2+ and 2 electrons. Because Zn metal can undergo chemical reaction to produce them. Don't say this in the exam though. Zn metal and Zn2+ ions are quite different things, and you can't simply say "Zn is *made up* of zn2+ and electrons". However, it can be formed from them under a redox reaction.