Re: How to find number of Reference Planes passing through a selected wall.

Use the geometry of the wall and reference planes.

Get the location of the wall:

LocationCurve l = wall.Location as LocationCurve;

and check against all the ReferencePlanes in the document:

FilteredElementCollector coll = new FilteredElementCollector(doc).OfClass(typeof(ReferencePlane));

and now foreach ....

Hope this helps.
Christian