Skin delamination will show as a low "bubble" (slightly raised area) in the skin, usually only 1/8-1/4 inch above the surrounding area. Some may be noticeable only when looking down the side in morning or evening light, when the low angle of light casts a more visible shadow. If caused by a simple gluing failure, it is possible to put small holes or a slit on the outer skin and inject glue underneath, then press it back down and [somehow] firmly clamp until dry. If necessary, put screws in to hold it in place and then remove them (or file off the heads) once the glue dries. Fill the holes/slits with a fiberglass gel coat repair compound afterwards. Or you can just live with the delamination - you won't even notice it after a few weeks and it generally does not spread any further.
If the delamination was caused by a water leak, obviousy the leak has to be found and fixed first. Then you have to figure out if there is any sub-surface damage, e.g. rotted wood panels or structure and repair that, which may require removal of a piece of skin. You may be able to cut out the skin out in 1-2 pieces, repair the damage and then re-attach the original skin to cover most of the opening. Use gel coat repair to fill the seams. More likely, though, you would be in for a fiberglass repair job and repaint of the area or even the whole side.