The 98 models (Gewehr 98 and Karabiner 98) were all manufactured in 7.92x57. Some K98 carbines were later rechambered for the 7.62x51 NATO cartridge, but these are visibly marked as such.
Somewhere on the rifle (usually on the underside of the barrel), there will be an importer's mark, which will identify the importer, country of manufacture, and cartridge the rifle is chambered for.
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