My boyfriend has chronic gagging. There is no heartburn no throat clearing sometimes he coughs alot. The gagging happens at anytime. He smokes and he can't smoke without gagging. Can I have a list of things this could be? He doesn't have any symptoms of a

Several. The smoking is an irritant. It can increase secretions. It can cause acid reflux. It can cause swelling of the throat and lymph nodes around it. It stimulates the gag reflex. It took me years to stop. Be kind. Patches seem to work since they don't jerk your nicotine level up and down. Keep using them for 2+ months. Have a doctor look at his throat if it gets worse or does't improve.
Quit smoking. Smoker at risk of esophagitis, gastritis, hoarse voice, chronic gagging and cough (as you described), cancers (oral, tongue, vocal cords, lungs, esophagus, stomach, bladder), emphysema (chronic cough), asthma. This is a potentially serious list. Get help.