Where to find the data sheet for Huawei Honor 6 smartphone?
There is no such thing like "datasheet for phone".

Phone is consumer electronics. Consumer doesn't have to know all these things. All you can/should get from manufacturer is manual (that usually says: "use original battery charger").

I would not recommend trying to power phone from 12V even if you are sure that there is BQ24190 chip, because you don't know what else is there. Maybe some zener diode that will blow up without any other damage, maybe some extra ESD protection designed for 5V and you will destroy whole ESD circuitry).