hi im wondering how do you make a photon cannon without a pylon.
I saw a couple in townwars im wondering how to do it?

make a trigger that enables doodad state for the cannon every trigger cycle. You'll want to have it preserve because any trigger that creates a unit will disable it again. I'm not sure but I think you have to enable for EVERY cannon, so the action doesnt work if you run it only once at a location where there are two cannons.

I think it stays enabled until you create or remove/kill a unit/building (which is usually often enough to want to keep in enabled every other frame).

What Sam said.
You need to cycle through the cannons unless you can spare have 1 location per cannon. The cycling is done by centering a burrowed zergling under each cannon and then center on the first ling, enable the cannon there, give the ling to another player and then center on the next ling, and so on. Until you gave all lings to the other player. Then give the lings back and repeat the cycle.

This would enable 1 cannon per trigger loop which can be fairly slow for a large number of cannons, so you you'll have to create many copies of the trigger.