Can smoking synthetic marijuana show up in a semen analysis ?

Yes: If it has thc, then it will show up - that's what they're testing for. If it doesn't have thc, then maybe not - but then what would be the point of smoking it.

No: Semen analysis does not have the same purpose as a urine drug screen. It focuses on other things directly related to sperm -- including their number and activity. It does not automatically test for substances like thc, either actual or synthetic.