Does multiple Trinity Forces stack hold points if they are equipped to the same unit and it holds?

Yes, multiple Trinity Force cards stack their effects when equipped to the same unit.

According to the rules of equipment, when you attach an equipment card to a unit, its effect text is appended to that unit's rules text (RiftJudge FAQ #225). Because each Trinity Force provides its own triggered ability ("When I hold, score 1 point"), a unit equipped with two copies of Trinity Force will have two separate instances of that triggered ability.

When you hold a battlefield, both instances will trigger, allowing you to score 1 point for each Trinity Force attached to the unit.