skate on (something)
To use roller skates, inline skates, ice skates, or a skateboard on some particular surface or area. You've got to be absolutely sure about the thickness of the ice before you go out skating on the frozen lake. We've had a real problem with kids skating on the long handrails of the staircase that leads up to the entrance of our office building.
skate on something
to skate on a particular surface. You can't skate on that ice! It's too thin. Don't skate on the ice until it has been scraped smooth.