How did nuSpock know about the Jellyfish?

[TEACAKE'S PLEATHER DOME]

The Quintossential Spock!

This is so awesome it should immediately bloom into common usage.

Quintossential

 

[battrekker]

We know that he didn't know because he specifically said it in the movie. As soon as they boarded the Jellyfish, Spock was concerned because he was expecting it to be of Romulan design. He didn't know if he would able to make it work. He also had to ask the computer where the ship came from.

From there, he inferred enough about the ship to carry out their plan.

Very clearly I heard NuSpock saying that (or asking if, not sure) Kirk had not told him everything he knew about the situation.

 

[MvRojo]

Also when Kirk and Spock boarded the Narada they disabled a Romulan lackey with whom Spock mindmelded. Via the mindmeld, Spock determined the location of both Pike and the red matter (jellyfish ship).

This is the exact explanation.