AFAIK, CR question should not involve any external knowledge.
But I have a hard time to figure out what the "basic" knowledge I can use to analyze the problem is.
Any hint/tip?

Generally, yes, both CR and RC are not supposed to involve any outside knowledge. Having said that... the line sometimes seems a bit fuzzy.

The test will expect you to know definitions of various words and concepts. For example, it if talks about profit, it expects you to know that you calculate profit by subtracting costs from revenues (and this could factor into your analysis). The test will not expect you to have knowledge beyond this, though - eg, if an argument mentions something about environmental problems, the test will not expect you to know all about global warming or that humans have a large (and largely negative) impact on the Earth's environment, etc.

Technically, if you think about it, although most people "know" we've got environmental and pollution problems, there's a lot of debate about the whats and whys and hows - so what do we really know? But we do know that, by definition, Profits = Revenues - Costs. No debate, argument, or possible alternate interpretations there.

In general, err on the side of "I know nothing but what this tells me, as well as any definitions I know for various terms / concepts." Be very literal and very critical. :)