Its not in China's interest for Israel to have a nuke, you talk as though China need a country to be fully cooperative to advance its interest.It's also not in China's interest for Iran to build a nuke
If Iran really legit go to that route, don't be surprised if it turns a blind eye to a full US attack against it.
It's imperative that Iran doesn't build a nuke as it would destabilized the entire Middle East and consequences would then flow to Asia as well (think S.Korea, Japan, Vietnam, Indonesia etc).
Iran should be more cooperative with China, but at end of the day its the west and Israel that ls China's enemy