Unless you have special plasters, cuts and scrapes on your knuckles are really annoying to deal with. If you need a knuckle bandage, you can modify a typical, rectangular plaster with a few cuts from a pair of scissors. This video from youtuber CrazyRussianHacker demonstrates a few tips for modifying standard plasters to be more useful for different types of cuts, including one for your knuckles. Grab a wide, rectangular plaster, then cut some triangles out of two opposite sides (so the points of the triangles are facing each other). Now you'll be able to wear the band-aid over your knuckle and it will stay on when you move your finger. If you don't have any band-aids at all, some athletic tape might be able to help with tricky spots as well.
You've Been Applying Band-Aids Wrong [YouTube]