If I Heedless Resurrection kill a rift herald to use his deathknel to summon a baron is the new location conquer done before heedles resolves or after

Before — the Rift Herald's Deathknell resolves first and Baron's entry (and that Conquer) happens while Heedless Resurrection is still on the chain.

Heedless Resurrection is already on the chain when you pay its cost, so killing the Herald as that cost makes the Deathknell trigger a pending item added above Heedless (Rule 808.1.d.2). Resolution is newest-first, so the Deathknell plays Baron, his "as you play me" replacement adds the Baron Pit and he enters there — establishing control and Conquering that battlefield — and only then does Heedless Resurrection resolve and return a unit from your trash.

Two notes: Deathknell only ignores Baron's Energy cost, so you still pay his 3 [C] Power, and that Conquer is subject to the once-per-turn scoring limit and the Final Point requirement (FAQ #12362).