Summitry is a complicated and lengthy process, expert teams specializing in diplomatic nuance and intelligence make a career of this, it takes many months (even years) to put these things together, the heads of state involved appear at the 'closing', they have scripted roles, each team has worked on every detail and there are not supposed to be any surprises. Trump is dispensing with all of this, he has little respect for the intelligence community (not without reason) and not much tolerance for diplomatic nuance either. My concern is that he goes into this expecting to come out with a clear and simple deal; denuclearized North Korea. What does Kim want and what will Trump offer to get this deal?
Kim has indicated he wants "denuclearization", but to North Korea this means the removal of any nuclear weapons and anti-nuclear weapon defenses threatening them, while for the US this means the cessation of North Korea's nuclear program and the destruction of it's nuclear weapons. Can these two meanings be reconciled? Can Trump agree to remove anti-nuclear weapon defense systems from South Korea in exchange for the elimination of just the North Korean nuclear weapons with the range to hit South Korea? Would an agreement to eliminate only short range nuclear weapons that could be used against just South Korea merit the US removing all anti-nuclear weapon defenses from there?
I expect Trump would seek the elimination of any nuclear threat to the US first, North Korea's capacity to strike the US with a nuclear ICBM is not that clear, they don't have long-range nuclear bombers, their submarines are not that sophisticated and their rocketry is notorious for it's failures. With an estimated 20 warheads, if 6-8 are on ICBMs and 3-4 make it to target, presuming they detonate it is a disaster of monumental proportions, but Kim won't survive. What is it worth to eliminate this threat? Should Trump agree to remove long-range nuclear bombers from Guam and Japan, promise not to target Kim with ICBMs from the US too?
Conventional forces could also be negotiated, no doubt Kim would seek US withdrawal from South Korea, would he reduce his military to a level similar to South Korea's alone? The details here are intricate, how does firepower compare? How many soldiers per artillery, are troops matched per capabilities, how does distance from the border factor, are naval and air force capabilities balanced, what about range and firepower?
The economic sanctions are another issue, there's a great range of these, one would expect Kim to agree on the restrictions on nuclear technology and materials, that he would neither import no export any of this, what could he ask for in exchange? Would an end to the interdiction by US Coast Guard of high seas ship-to-ship cargo transfers be enough, or should North Korea be allowed to freely trade? Economic sanctions are by multi-party, does Trump have the international community on board with whatever deal he makes?
I think the best we can hope for is an understanding that Kim wants a way out of the current predicament and agrees to work with Trump towards that goal, a 'roadmap' of steps North Korea promises to undertake and a commitment from Trump certain milestones will be rewarded with diplomatic recognition, reductions in forces and removal of sanctions.