A BRep (short for boundary representation) is a 3D modeling umbrella term that typically includes both surfaces and polysurfaces - so if you have an open BRep from a GH loft component, chances are it's a surface. You should be to connect your Loft component output into the S input of an SDivide component to perform the surface subdivision.

If further surface operations need to be performed (reparameterization, for instance) you could always use a surface collection (Srf) component as an intermediate piece in your definition.

It's possible that your open BRep loft output is a polysurface (if your lofted curves are 1 or 2 degrees, if you used straight or developable loft options, etc.) in which case you would want to place a BRep Components (Explode) component between your Loft and SDivide components to break the polysurface down into its component surfaces (they would have to be subdivided separately).

If you want said polysurface to be a single surface (though depending on what you're doing this may not be possible) it would probably be a matter of changing loft options or rebuilding the original curves as 3 degree curves and re-lofting.