What energy type does poison use and does it stack?
Pokemon TCG is quite different than the game. There's no "poison" type like in the game. In TCG, poison is a status. So, even if the defending pokemon has psychic resistance, it doesn't cut the poison damage, even if the poison is afflicted by a psychic pokemon.*)
No it doesn't stack.


I suggest you to read the basic rulebook again, it's very clear on what poison do there. I learned almost everything from the rulebook. But, since I am an old pokemon player (last played 4-5 yrs ago), so I forgot what poison exactly do. But AFAIK, it damages the affected pokemon between turns.

*) This is different if Spit Poison has initial damage attached, for example, 30. So the initial damage will be 10 (30 original - 20 resistance), aside from the poison status damage.