To snap an X Y position the basic idea is
so for a 16x16 grid it's
But depending on your objects origins you may need to add an offset
or instead of round use Floor or Ceil
In your example lets say "character" and "spawn_object" both have centered origin points. It's a 16x16 grid and you want it placed in the center of the tile. you would put an action like this.
system create "spawn_object"
hope that helps.
: I should mention I'm using "system create object" instead of having the "character" spawn the object. That way It can be done in one action with an expression instead of spawning the object then snapping it's position with a second action. Also when one object spawns another the spawned object inherits it's rotation. Your example didn't mention wanting that.