What height/ distance from ceiling or above surfaces would be good for uplighting/ scone wall lamp?
You're first consideration should be glare. Typically we try and set the best lighting above,slightly behind and on the right hand side of the head. This gives best lighting for reading or using a computer screen (for a right hander anyway). I have never seen a height requirement for a sconce from a reference source like the AIA. other than keep it away from head banging or a shoulder breaker. A fire egress would keep it above 7'4". In this case its not an egress so I would say use your best discretion. 

Hope this helps