Meyers Orts- und Verkehrs-Lexikon des Deutschen Reichs (Meyers Gazetteer), online edition, with GOV (genealogy.net) for post-1945 Polish equivalents · meyersgaz.org / gov.genealogy.net
Kosaken, Goldap, Gumbinnen, Ostpreussen, Preussen
Meyers page fetched this session; Nominatim reverse geocode of the point independently returns Kozaki, Gołdap County.