The question asked by IFLY was "How would a pilot ascertain that climb requirement is going to be met?". The answers so far haven't actually answered the question except perhaps sabenaboy's which alluded to experience being the only way and Intruder alluding to why that is. One way to find your all engine climb gradient, which charts for are difficult to come by, is to find the one engine out gradient and multiply that by 5. That gives a ballpark figure for a twin.