for the hull its different the end of a screw driver has always been my fave...just tap tap tap and loo(smooth) over with your hand
on the decks honestly I dont get it...its called a soft spot for a reason....you walk around the decks moving and putting more weight on one leg then the other, move around if you see or feel any movement mark the spot
then go below decks and look at cabinetry, and bulkheads or hardware if you have any indication of a leak...mark spot, go up again on deck and dance around...
if you have delamination you will hear cabinetry and bulkheads squeak when walking directly over it...if you have detabbed bulkheads youll feel movement like the deck hitting the top of the bulkheads, etc...
if all you have is a soft spot mid deck where no hardware or bulkheads or cabinetry is under or around it then its an easy real easy fix... if there is stuff under a simple task can become quite major
Im doing this as we speak on my islander 36
there is a forward bulkhead that rotted, so every time I walk over it it reminds me FIX ME!
new ply, re tab, glass and some varnish and thats that
the deck is solid it whats under that failed
on small places where its soft and you know its a cored deck and hopefully ply there are many ways simple and detailed on how to fix it
cheers and good luck