I think you can do this:
DWORD dwExStyle = ::GetWindowLong(m_hWnd, GWL_EXSTYLE);
if ((dwExStyle & WS_EX_TOPMOST) != 0)
{
// do stuff
}
Here’s the MSDN link – http://msdn.microsoft.com/en-us/library/ms633584(VS.85).aspx
And here’s the MSDN link to the extended styles – http://msdn.microsoft.com/en-us/library/ff700543(v=VS.85).aspx – topmost is currently listed as “TBD” 🙂