If your floor is not shaped then it could be as easy as reviewing the direction of the curve loops in relation to the face normal. Often (if not always) the outer loops are the first items within the array. I believe the openings are clockwise with respect to the normal of the face because the initial surfaces are formed in the anticlockwise direction. This topic has been covered previously.
If the floor is shaped then you'll need another approach because an opening would not necessarily be an inner loop within a single planar face. Where floor surface is triangulated a number of triangular faces would border an opening rather than that opening being within a single face.
Perhaps looking at the sketch geometry instead and analysing that to determine the outer loops would be the way forward for shaped floors.
You have a tiny strip of floor between what is presumably your stair riser and the perimeter of the structure, would you need to form that in reality? Some would treat that as a floor notch rather than an opening and so if the aim is to identify risers by openings then this highlights an issue with that approach.
