This is a reference post. The data below is taken from the "Data Appendix" in "Hive Mind" by Garett Jones, which I reviewed here. Click on the images below to make larger.
"Notes: The middle column reports the Rindermann, Sailer, Thompson cognitive ability (CA) scores estimated from the international tests the PISA, the TIMSS, and the PIRLS. The right-hand column reports national average IQ as estimated by Lynn and Meisenberg.The main take-home lesson is that countries differ quite markedly in their average IQ, pretty much as you would expect given their economic and political success or lack of it. Not forgetting that countries are people, not inert geography.
The table only reports data for countries where both estimates are available. Both estimates include data of varying quality; in particular, developing country estimates may be based on small samples or limited numbers of tests and should be treated with caution.
This is a problem that also arises when measuring GDP per person in developing countries, as Morten Jerven's book Poor Numbers documents. Sources: Rindermann, Sailer, and Thompson, "The Impact of Smart Fractions" and Lynn and Meisenberg, "National IQs Calculated." See also Jervens, Poor Numbers. "
The scores are misleading for countries which are highly stratified ethnically such as Israel, many countries in Latin America and the USA (to some extent). India (not shown) with its castes and jatis is problematic - the concept of national IQ doesn't really apply there at all.
China's average national IQ is generally estimated to be 105, aligned with Taiwan and Japan above.