When Jon meets Daenerys
They will realize that they are natural allies. Jon is the king of the north, has an army and is familiar with the territory (what else can he offer her?). Dany has dragons that can kill White Walkers with fire. She also has dragonglass that serves the same purpose.
But their objectives are different. Jon wants to fight against Night King's army and Dany wants to retake the throne. Basically, they want to head into opposite directions. Jon wants to go north and Dany wants to go south. If they are to become allies, one of them will have to postpone his/her plan in favor of another one's plan.
I don't see Dany being the one who will cave in, and Jon has already proven that he's willing to antagonize people (night watch) to go forward with his plans. Maybe their meeting won't end well and they will not become allies after all? Any ideas what might happen?