It depend on how suicidal they wanted to be.
A couple of years ago, during the 2nd intifadah and the 2nd Gaza war, Hesbollah (from Lebanon) shot some conventional rockets from the lebanese border into Israel. That was at the same time that Hamas was shooting rockets into southern Israel from gaza.
The hesbollah rockets landed in Haifa, in various places in northern Israel, and a few near the airport.
The hamas rockets landed in various places in central and southern Israel. They didn’t do any serious damage, although they were annoying.
The important point is that neither Hesbollah nor Hamas shot rockets towards Jerusalem. Simple reason: their rockets were not all that accurate, and there was just as good a chance that the rocket explosions would have killed palestinians instead of Israelis. Or worse yet, the explosions might have hit Al Aqsa or the Dome of the Rock.
Then there would have been hell to pay.
So… to answer your question, I can’t see of a situation in which any country nukes Jerusalem, unless it was a nihilist that wants to blow up the entire Middle East.