i looked this up after getting an argument w/a european relative. im american.
"Founded in 1917 as Nippon Kōgaku Kōgyō Kabushikigaisha (日本光学工業株式会社 "Japan Optical Industries Corporation"), the company was renamed Nikon Corporation, after its cameras, in 1988. Nikon is one of the companies of the Mitsubishi Group. The name Nikon, which dates from 1946, is a merging of Nippon Kōgaku (日本光学: "Japan Optical") and an imitation of Zeiss Ikon. The Japanese pronunciation is [nikoɴ]; the British pronunciation /nikon/; in the United States people say /ˈnaɪkɒn/.
I pronounce it like any other american. Although, since I am studying Japanese and know what it should sound like, I will probably alter my pronunciation when in Japan next year.