What percentage of the worlds population have caught Covid-19, as of August 22, 2020?

That’s hard to say, since 80% are reportedly asymptomatic.

If you want super rough estimates, google says there are 23 million cases worldwide. Google also says there are 7.594 billion people on earth.
Plugging that into a calculator, 23 million is 0.30287068738477746% of 7.594 billion

Meaning that in very rough numbers because @filmfann mentions asymptomatic people and that means the 23 million confirmed cases isn’t 100% accurate when you count in asymptomatic carriers, 0.30% of the worlds population has COVID-19.

This is as of August 22, 2020 at 7:11 PM. I googled the number of cases and I googled the worlds population. So again, this is a very rough answer and excludes all asymptomatic and un-diagnosed carriers.