How do you say Tiffany in Japanese?

ティファニー /ti fa nii/.

Note than 'fa' syllable (ファ) in Japanese is a 'digraph' made of two parts, 'fu' (フ) and 'a' (ァ) so it sounds something between the two (and 'fu' in Japanese is pronounced something between 'hu' and 'fu'), rather than a simple 'fa'.