Jumping behaviour may suggest the fish have a problem with parasites, or the quality of the water. You will also see fish jumping when the pH is dropping, or when some other irritant is accumulating in the water, like Ammonia. So, the first things you do are water tests. Then, if nothing is found, please consider that parasites, particularly with Flukes as these can and do cause jumping. 

It is assumed that the hope is that when the fish is jumping that this will dislodge the parasites that are worrying or annoying the fish. Instead, it often leads to a fatal crash into the pond walls or other objects, be sure that it there is anything in the pond that a koi can hurt itself on .. it will find it .. it is even possible, as has happened on many occasions for the koi to jump completely out of the pond where a great deal of damage, and even mortalities occure. So, establish water quality first of all and then treat for parasite that is probably causing this jumping. 

Salting your pond can help with this problem ... but cannot be guaranteed.