Right fork mounting point
Hard to tell from the photo whether a light or something else was mounted there in the past. It's certainly possible. 

There aren't any modern lights I'm aware of designed specifically to mount to the side of the fork like that. Many dynamo hub lights are designed to mount to the joint of the left/right sides (i.e. the crown) of the fork, but that type of mount wouldn't fit well on the side. 

It would be fairly easy to take a small piece of plastic or metal tubing and an appropriately sized screw, and create a small mount that a regular bike handlebar light mount could go on. For a step-by-step example, see this blog post. Below is a picture of their final setup: