This is a front section of one frame rail. The side facing the camera is the top; the broad notch in the top is the saddle where the cylinder assembly rides. The machinist is probably laying out the locations of bolt holes which must be drilled for the attachment of the cylinders and multiple other parts, including spring rigging, a cross-member for supporting the pilot truck, and the pilot itself. White paint was applied to facilitate marking the hole locations.

I think the front is to the left, in which case the right end will be welded to the existing frame where the damaged section has been cut off.