i conquer with a unit and last rites attach, the bf is veiled temple, can i trigger last rites and detach it ?

Yes — both triggers fire at once and you get both, in either order.

When you conquer Veiled Temple, Last Rites' "when I conquer…play a unit from your trash" and Veiled Temple's "ready a friendly gear; if it's an Equipment, you may detach it" trigger simultaneously. You control both, so you choose the order they go on the chain (Rule 383.3.d).

If you resolve Veiled Temple first and detach Last Rites, the Last Rites trigger is already on the chain and still resolves — detaching doesn't counter it, and the gear stays at the same location (Rule 435.4), so it doesn't need to stay attached for the ability to finish. One cleanup note: the now-unattached Last Rites is a non-Unit Gear sitting at a battlefield, so it gets recalled to your base in the next cleanup (Rule 457.1).