The elbow is one of the places pressure sores form — the bony areas with less tissue under the skin to pad the area, along with the buttocks, hips, heels, ankles, shoulders, back and back of the head. If that is what this wound is, the signs to watch for are the ones for pressure sores.
Contact your provider right away if you develop blisters, an open sore, or any signs of infection, such as a foul odor from the sore, pus coming out of the sore, redness and tenderness around the sore, skin close to the sore that is warm or swollen, or fever.
What makes the elbow unusual among those sites is that you put weight on it on purpose. Lying still puts pressure on a heel or a tailbone. An elbow is pressed down every time someone pushes themselves up in bed or leans on a chair arm. The cause is the same either way — pressure sores occur when there is too much pressure on the skin for too long — but the fix is about how you move, not only how often you are turned. Both matter: change position often, and avoid slipping or sliding as you move positions.
It is also a spot you can see for yourself, which makes the early stages worth knowing. A stage I sore is a reddened, painful area on the skin that does not turn white (blanch) when pressed. At stage II, the skin blisters or forms an open sore. The area around the sore may be red and irritated. Catching the first of those is the whole point of looking.
An elbow wound may of course be something else — a graze, a cut, a surgical incision. If so, the general signs apply instead: redness with increased pain, yellow or green pus, or excessive clear fluid around the injury; black edges, which signal dead tissue; bleeding that will not stop after 10 minutes of direct pressure; fever of 100°F (37.7°C) or higher for more than 4 hours; pain that will not go away even after pain medicine; and a wound that has come open.