How is my current allocation - 50% Vanguard S&P 500 ETF (VOO), 30% Invesco China Technology ETF (CQQQ) and 20% NikkoAM-STC Asia REIT (CFA)? Is it diversified enough?

It is underdiversified,

try to shift much more towards IWDA.

30% CQQQ is super high risk, if China exposure essential

You could do of the 30%

-10% CQQQ

-10% PGJ

-10% KURE

still risky

The REIT sector could be streched from Asis by an additional a mix of VNQ and IQQP,

or a global REIT ETF in the first place.