This question will resolve as YES if any nuclear weapon is detonated anywhere in the world after January 1, 2023 and before July 1, 2023. Otherwise NO.
A test detonation would result in the question resolving as YES.
A detonation would resolve YES regardless of whether it is deliberate, inadvertent, or accidental/unauthorised
Detonation means nuclear explosion. If a nuclear weapon were launched/dropped/etc but the nuclear weapon did not detonate (due to malfunction, interception, etc), that would not count as detonation. If a conventional explosion occurs but no nuclear explosion (for example, a dirty bomb that distributes radioactive material with a conventional explosion), that does not count.
Related questions
See https://manifold.markets/post/nuclear-risk-forecasting for a dashboard of other nuclear risk questions along with commentary and analysis.
Polymarket is currently having this at 5%: https://polymarket.com/event/will-a-nuclear-weapon-detonate-by-june-30