Step 1, unclog with a pin. I use one from an old work badge so I have something to hold to wiggle around around and pull out.
Yeah, I know how that sounds but that is what I do. So, there it is.
Step 2, if the pin doesn't unclog your clog, cut the tip. Yes, I know how that sounds too. At this point I'm giving drbindy an aneurysm. But if the clog is bottle necked at the opening, make another opening. Although I do suggest cutting it at an angle because the hole will be bigger.
Step 3, if it continues to clog, find yourself a mixing stick to paint the glue on. I have a supply of coffee stir sticks that have come in handy for this. And because they're pretty much free with a cup of coffee, I don't mind throwing them away after a project or two. Worn out paint brushes also work very well for this purpose.
Step 4, buy new glue. It is ok. You did everything you could to use every last drop. But at this point, you have to come to the realization that there are other bottles of glue out there looking for a good home. Say farewell to your little friend and bring in a new friend.