Antique chef knife marked M Schlesinger Berlin C., Rosenthaler Str 63-84 (?) and GF inside an oval. These markings have no references that I can find and I suspect that M Schlesinger was a retailer and GF is the maker. Inside the heel is the mark “Guy..” which is most likely the G in GF. The style of forging and the style of the mark GF, Guy and the name Guy suggest French manufacture rather than German. German knife makers certainly made these rat tail tang AKA ‘Nogent’ style knives.
Blade is a hand forged carbon steel with a thick spine and heel and a thin graceful tip half. It has been sharpened down a lot and is much narrower than original, it might have been originally 2.5” wide and is now 1.75” wide at the heel. The handle looks to have been replaced a long time ago as well. The original handle had a birds beak pommel rather than the straight handle it has now, the nickel ferrule ring is original.