How can I drill a grommet hole in my Ikea desktop?
Of course you can, and it's very easy to do.

All you need is an appropriate hole saw.

Drill from the top down.  If you can, hold or clamp a piece of scrap wood under where you are cutting.  That will prevent the bottom from splintering.

Then to make it really look nice (and prevent any future splinters) you'll want a desk grommet that slips inside the hole.  Make sure you match the size of the hole and your grommet.