How do you pronounce S'chn T'gai?

Answer 1

I don't know because in TOS episode "This side of Paradise", Spock said that his full name was unpronounceable to Humans.

Answer 2

my best guess would be s'chn as similar to chet, with a harsh ch. T'gai, I imagine, is T'gey, with a hard A. In total, I imagine it to be s-CH'n t'gey. This is mostly speculation, though.