닦다 = to clean/wipe (surfaces), can be used for the floor, a table, a counter, your teeth, etc.
I'm actually genuinely curious because my son is learning to do bathroom stuff and he's learning Korean with me.
What a weird sentence. I though maybe it was some weird insult because no one ever just says "wipe!"
It is casual imperative form. 닦아 = casual 닦으세요 = polite 닦아라 = formal low 닦으십시오 = formal high