Functional Currency translation Gain/L

Hello!
My name is dennis. I have a int'l tax question for reporting foreign currency exchange gain.

Here is the case: A China Citizen with 9 yrs green card in US. He seldom comes to US. He bought a china stock at 8M rmb the translation spot rate is 1usd vs 8 rmb before he got green card. He sold out the stock for 7M rmb but never exchange into USD. the translation spot rate is 1usd vs 6.2 rmb this year.

RMB 7M-8M=-1M (LT CAPITAL LOSS)
USD 1.13M-1M=130000(CURRENCY TRANSLATION GAIN)

Questions:1. Which functional currency he should use for file his us tax return?Should he report the phenomenon gain?
2. If he sold out for 9M rmb instead of 7M, should he report the currency trnslation gain?
3.bought the china stock after getting the green card anything reporting difference?

Thank you!

Functional Currency translation Gain/L