It is hard to make a good recommendation based on so little facts. I would look for a nice prime lens as this might be the closest thing to what he probably needs, but what is your budget? What is already in his bag and what are his favorite photographic subjects and does he aim at slides, CN or b+w and/or what is his favorite print-size? As a gift I'd consider something like a 1,8/85mm or a 1,4/50mm or the alike (something impressive and shiny ) but this may be far away from what he has in mind.

best

Stefan