Did the targeted killing of intellectuals during the reign of the Khmer Rouge in Cambodia and the Cultural Revolution in China have a measurable long term impact on the overall intellectual capacities of these nations?

Intellectual capacity is relatively subjective and hard to quantify. However, it would be reasonable to suggest that the long term impacts of these events has been stifling on their populations.

I'm not qualified to comment on the Cultural Revolution, but I've come across a couple of sources that touch on this theme for the Khmer Rouge.

Joel Brinkley explores the hereditary nature of PTSD in Cambodia's Curse. He references a variety of studies that suggest the children of a traumatised generation are likely to be more mentally volatile. Hence, it could be reasonably argued that this has stifled the "intellectual capacity" of Cambodia.

Brinkley and David Chandler (a go-to for Cambodian history and culture) both insinuate that apathetic mentalities are more visible traits than a lack of raw intelligence though. Both conclude that Cambodians just want to be left alone, but that by no means correlates with a lack of intelligence.