Potential event horse or jumper
High shoulder point (the front of the shoulder is high, with a steeply angled humerus from there to the elbow; this ensures scope over large jumps)
Uphill build
Medium bone structure (extremely fine bone structure is less likely to hold up)
Short- to medium-length back
Short- to medium-length pasterns (long pasterns tend to break down)
Well-set knees (horses "straight" in the knees are prone to knee injuries)
Event horses can range in height. Note that larger horses (in height and mass) can be more difficult to keep sound as they are harder on their legs and feet
Movement
Event horses need to be very athletic with fluid gaits. Prospects should have more "action" at all three gaits than, say, a hunter (see below). This often indicates it will be easier for them to move with impulsion in the dressage ring and that they will pick up their knees better over fences.
Personality
Brave, athletic and hard-working. Event prospects need to be bold, brave and forward-going horses that have good endurance. Many of these horses could also be described as "proud" or "arrogant." More energetic horses are often possibilities--as long as they are mentally sane and have a good work ethic, the extra energy is beneficial on the cross-country course.
Injuries to Avoid
Breathing issues
Severe tendon injuries (mild strains or bows are generally not an issue if given enough time off prior to retraining)
Severe suspensory injuries
Joint chips or fractures
Vision limitations