I can see some discoloration I can only attribute to glue. I have some showing on my finished boat and as I plan on making another, I was wondering, ??How do I know that I have removed all glue from the surface of my boat by cleaning and sanding the wood surface prior to glassing??

I wiped with a damp cloth during stripping, washed lightly with a little bleachy water and sanded the hell out of it. Dusted, wiped, and tack clothed the hull and still had a little glue I could not see until the epoxy brought out the colors.