1.What are the best, most comprehensive and up to date resources regarding the demographic future of Europe?

No clue.

2.If IQ is heriditary then how come Middle Easteners, who cluster closely with Europeans JPG in genomic studies, average around the same IQ as African Americans?

Heritability doesn't mean that clustering together means having the same IQ. I probably cluster very closely with Magnus Carlsen, but his IQ is probably 60-80 points higher than mine. Heritability just means that your trait will be more similar to your identical twin.

Also, the brain varies more than the overall genome, so overall genetic similarity doesn't necessarily imply brain similarity.

3.How would you respond to studies like this one that argue that twin studies are methodologically flawed and therefore should not be used as proof for there being a genetic component behind IQ differences between racial groups?

Let's have a look.

Today, this methodology has been largely replaced in favor of contemporary molecular genetic techniques

This is a lie. Molecular genetics make worse predictions than quantitative genetic studies (aka twin studies) and this is well known by everyone. Molecular genetics studies are cited to see how well we've progressed at using molecular genetics, not to actually predict what the world is like.

heritability studies have seen a diminishing role in behavioral genetic research of the twenty-first century.

I doubt he has a citation for this. I think he just assumed this would be true based on his lie. If you can find a non-paywalled version of this study and tell me what evidence he cites, I'll consider it but my prediction is that this will be asserted without evidence. I'm busy right now, but try typing the doi into sci-hub. Let me know what (if anything) he writes about this statement.

One important reason the twin method has been superseded is that it depends upon several questionable assumptions, the most significant of which is known as the equal environments assumption

There is no equal environments assumption in twin studies. We just measure how different the twins are from one another. We know it's not perfect, but we also know the numbers give reliable predictions despite their imperfections.

Here, we review the evidence presented and conclude that these attempts to test the equal environments assumption are weak

Who cares if attempts to prove equal environment are false when the assumption is not "crucial" like this author says?

You measure people with identical genomes. Intelligence is 80% more similar than to the general population. Now let's grant the assumption that we know for absolute certain that the environments are very very different and not at all similar. Who cares, we still measured 80% more similarity based on genes. No assumption necessary.

Also, this author's rhetoric is kinda dumb. In the very different environments assumption version of this, the logical conclusion would be that heritability is underestimated because more similar environments would lead to IQs being even more similar. He didn't think this one through.

We conclude that the equal environments assumption remains untenable, and as such, twin studies are an insufficient method for drawing meaningful conclusions regarding complex human behavior.

Again, total non-sequitur.

Why would different environments invalidate the measured numbers? Are people with similar genetics not actually having more similar IQs? Like ok, different environments. Whatever. The numbers are still there and still predict the world around us.