Not much, really. They will ask you about some C++ details, which are mostly found in any C++ book and specially in Effective C++, and a couple of very shallow OO design patterns questions. The hard thing is actually refraining from trying to do anything meaningfully interesting in the exercise: don't. Need to iterate over a grid or matrix? Use plain C in a tight loop, with hardcoded values. Throw in some mostly uninteresting use of STL data structures and avoid entering the template realm or some other convoluted design and you might be OK (since the whole assessment thing is opaque). Other than that, the culture is OK for young and inexperienced people, with most senior people noticing the bad smell and leaving sooner rather than later.
