The 1 to 10 scales are tricky. My rating would be 5 is use professionally or equivalent, 7 build non-trivial app and maintain legacy code, must know best practices and style guidelines, basically able to work in a large code base with other users. 9 would be contribute to the language or at least be involved in the community. But I don't know if everyone has the same interpretation of the scale, so you could be relatively competent but only rate yourself a 5 or 6.

Serious question, if the person actually had a 9 out of 10 knowledge of C++, how would he answer? Or is this just a teaser question?

I don't know C++ but I would answer pointers are addresses in physical (?) memory. They let you pass around variables by reference where the receiving function has full access and permission to edit its content. Pointers have to be dereferenced with the appropriate type before being able to read it