What important information does Johnny’s spy-helper give him? How is this information gotten? From chapters 7-8

This isn't from chapter 7 or 8. I'm thinking you might mean chapter 9. Johnny must stay close to Dove, who might have information if Colonel Smith is planning an action against the rebels. With the help of Lydia, Johnny discovers a shredded note that Colonel Smith wrote to Lavinia Lyte, who he is courting. Together with Rab and Uncle Lorne, Johnny puts the note back together and figures out that Colonel Smith is going to be part of a large raid on Portsmouth, sixty miles north.