ARNSWALDE/CHOSZCZNO is located at 53-10-00-n 15-25-00-e, due west of PILA and southeast of STETTIN/SZCZECIN, Poland.
I was unable to locate a Schlagentin, however, when I used "wildcards" I did come up with a lake in the immediate area (close enough to be within the Kreis) called SCHLAGE SEE (53-00-00-n 15-49-00-e) now called JEZIORO SLOWIE. Maybe your ancestor's location had something to do with being near the lake. If you go to mapquest.com and follow the links to "maps" and "latitude/longitude" and put in the coordinates, you will get a map showing you where it is. Sorry I couldn't do better....Happy Hunting!