How do I determine where my mucus comes from. I get my mucus from making a snort or also "reverse swallowing". Is that from my nose?

Tough to say. Mucous from snorting almost certainly originates from nose. If its from the throat it could be coming from either location. Try nasal saline first. Need to see someone to determine if it is due to allergy, sinus issue, or acid exposure to throat. Could be more than one reason.
Post nasal drip. Sounds like it is in the back of your throat.