weird combo, i know, but if I have a sprite on a field and i play Vi with Ambush (pacekeeper) do I score from holding? ( I am playing lux)

No — playing a unit never scores a Hold. Hold is checked in one place only: the Scoring Step of your Beginning Phase, and only if you still maintain control of that battlefield at that moment (Rule 471.2).

Since Ambush requires playing Vi to a battlefield where you already have units, that battlefield is one you already control — so there's no Conquer happening either. Nothing about playing Vi, or being on Lux, changes the timing of when points are awarded; you'd just have Vi sitting there.

One catch worth knowing: if that Sprite is your only unit there, a lone Sprite can't ever hold on its own — Temporary kills it at the start of your Beginning Phase before scoring, so the battlefield is empty when the check happens. Vi, Peacekeeper staying on board is what would let you actually hold it on your next Beginning Phase.

If the "field" is instead a battlefield you don't control (so the Sprite is contesting it), then the only way to score there is by winning the resulting Showdown/Combat and Conquering — that's Conquer, not Hold, and Vi's Ambush doesn't accelerate it.