In Chinese, you don't say anything in response to a sneeze.
bi'u
Before I really knew what 'bless you' and 'gesundheit' were really expressing (that i'm wishing they were healthier), I just thought it was a polite way of acknowledging a sneeze occured. Maybe one translation could be { senci } (Sneeze).
bi'unai
If a Chinese person hears { ko kanro }, I imagine they'd call malglico (or rather, malropno) foul.
One similar situation might be for the english _expression_ "Brrr," for which (likewise) there is no Chinese equivalent. One translation of 'brr' into lojban that might make sense to a Chinese speaker is { lenku } (Cold).