If you have the DLL source, it's easy, just place a breakpoint in any of the entry functions within the DLL and see when it's getting called. You don't have to have the source for the executable, just need to tell VisualStudio what exe will be loading your dll. If you don't have the exe or the dll code, I don't believe there's anyway of telling when the executable is making those calls (other than reverse engineering the executable).