I can react temporary sprite in beginner step playing Janna and win by hold?

Yes — as long as you control that battlefield. Janna, Savior has [Reaction], so she can be played during the Closed state created by the Sprite's Temporary trigger in your Beginning Step, and she'll be placed at that battlefield (units played at Reaction still go to your Base or a battlefield you control — Rule 813.3.a).

She resolves first off the chain, then the Temporary trigger resolves and kills the Sprite. Since Janna is still sitting there, you never lose Control, so you Hold the battlefield in the Scoring Step (CR 190.4.a, 471.2). Same interaction as reacting with a hidden Teemo (FAQ #1199).

Two notes: this must be the battlefield you control — you can't drop her onto a contested or enemy battlefield, so it won't work if the Sprite was there without you actually controlling it. And a Hold point at match point does win the game; the "score every battlefield" restriction only applies to a Final Point gained through Conquer (CR 473.1.a.1).