Which equation in general relativity predicted wormholes?

No equation - wormholes are cooked up. Wormhole metrics do of course satisfy Einstein's field equations but the process is more about creative ingenuity than about discovering some facet of the field equations stumbled upon by solving them. read more

If there is a prediction about wormholes it follows from taking the metric and matching it to a stress-energy tensor, in which case Einstein’s field equations will show that exotic matter is needed to hold the wormhole open. read more

This is what Ben is getting at in his answer. General Relativity does indeed predict wormholes, but only if you use input parameters that are physically meaningless (or at least currently believed to be physically meaningless). read more