Question=how do i get to
You get to Krokotopia by finishing all the quests in Wizard City. A good indication that you are close to finishing all the quests is that you have a quest to defeat Lord Nightshade in his tower. After this you will talk to Merle Ambrose who will give you a key to the spiral door for Krokotopia.
You'll find this door inside Bartleby.
In particular, you will find THIS QUEST. Once you get that quest from Merle, you're on your way!
Now, as I have said before, the other way to get to Krokotopia is to make friends with someone who will let you port to them in Krokotopia. Unfortunately you won't be able to do much there. It's best to do the quests.