Just about any situation you could ever think of. If it can kill someone, they could potentially need CPR. Car accidents, heart attacks, hypoxia, GSWs, organ failure, metabolic problems, [pregnancy or birthing complications, just about anything. If the patient does not have a pulse and is not breathing, they require CPR.
I think an easier explanation would be what are NOT situations that require CPR. That would be any time the patient is breathing and/or has a pulse, or if they have signs or injuries incompatible with life such as transection of the body, decapitation, rigor and/or lividity, decomposition, incineration, valid DNRs, and any other co-morbid factors.
Myself - I'm a paramedic