I try to clean my tools after working with wood glue but i always miss a spot here or there. My square is covered with wood glue because i didn't clean it fast enough. Whats the best way to take the glue off? I don't want to damage the plastic or metal on this precise part.
Bucket of hot water and a utility knife is what I use. Let tool sit in bucket. Sometimes after a couple minutes you can just touch the glue and it falls apart. If it is a strong glue it will pop off with the utility knife.
The hot water is the fastest way I know because it heats both the glue and the tool. Heating the tool causes its molecules to contract, weakening the bond and the glue just melts most of the time.
It depends what kind of wood glue it is. Polyurethane glue is very hard to dissolve with solvent. There are products made specifically for this difficult cleanup, but I have not tried any. One thing that did work for me was spray carburetor cleaner, but that is harsh stuff, I doubt it would damage the metal but it may damage the plastic.
Regular white or yellow wood glues are not so bad, I'd try soaking the square in paint thinner, but that might even damage some types of plastic.
For regular wood glue (like titebond or elmers), heat will soften it. Only question is whether or not you can find a way to heat up a particular tool enough without damaging the tool.
I would try a hair dryer or heat gun while being careful to avoid over-doing it.
For items that are likely to get glue on them frequently, many woodworkers use paste wax as a preventative measure. Things like clamps and squares used to square up a piece while glue is drying should have several layers of wax applied before use.