Hefty aluminum handle cutting tool.  The knob unscrews to remove or adjust blade.  The blade is 1/8" thick, both ends are ground to point on both sides, angle end and rounded end.  No markings at all on blade or holder. 

leather?

Yes.  If we don't know what it is - its either for leatherworking or a nutcracker!  Maybe its a nutcracker?  Smash the nut with heavy handle then pick out the nutmeat with the blade end.  But really, it could be for leather.  The blades aren't ground like a knife, it's too wide an angle.  And if it was a scraper it would only be ground on one side.

Seems it would be hard to use as a scraper. A scribe, or some sort of marking knife?

From the shape of the ends, it looks like a lathe tool.

Windshield knife?

maybe one of X-acto's odd hobby knives?