There are a few different ways to kill a terminator, most of which involve some sort of extreme force or explosives. For instance the original T-800 in The Terminator can be crushed by a hydraulic press as seen when it's destroyed at the Tech Noir club or by a pipe bomb (which it was using to target Sarah). Similarly they can be temporarily disabled with concussion and other forces such as the gas explosion that destroys the fuel truck or by being submerged in water, which is how Reese killed the terminator in the first movie.
Alternatively a gun with high damage per shot such as a pump or automatic shotgun can be adapted to fire small pellets of acid which can shatter and spray on or around the terminator to quickly deteriorate them. This would require a lot of ammunition so this might not be a good option if you want to carry a terminator around like a pull-string duck to take it from base to base but it could work well for an EMP attack or other forms of disrupting its circuitry.
If you have a weapon designed to kill drones then it can be used for the initial stage of getting a terminator's health down, but you will need to have the Mk14 sniper for the second phase of overloading its circuits. Regardless of how you do it though the best strategy is to just keep whittling down that blue bar of health until it turns red and it's time to use your Mk14.
