Stud on from ball joint will not come out

They can bind in the taper really tight. Usually I'll get them free using 2 large hammers. You put one hammer on one side of the knuckle where the stud passes through. Then give the opposite side a good hard hit. The idea is that the impact squeezes the hole and deforms it for a moment and it comes loose. Another option would be to use a torch to heat it up, the MAPP gas torches you can get in hardware stores will work for that.