In order to get the reward, when the event has already been completed in your server, you must step your character in the base floor of the cake in Cormaya, go to a town with a extraction machine and step on it, then go back to the cake, step on it again and go to a diferent city with an extraction machine. You need to complete the sequence in such a way that you step in every extraction machine.
An example of sequence can me: Cake - Carlin extrantion machine - Cake - Thais - Cake - Liberty Bay - Cake - Edron - Cake - Darashia - Cake.
Once you have completed the 'tour' you just need to ask for the 'reward' to the npc near the cake, choosing 1 item of these (cake cabinet, cake tapestry, and cake backpack), and one of these cupcakes (blueberry - mana, strawberry - hp, and lemon - distance skills)
In order to the world to complete the event sucessfully, 2 phases must be complete:
1) 200 sweet and sugary substances must be looted from the raids of cake golems, and delivered to the bakers next to the extraction machines. And then 200 cake golems must be lured into the extraction machines.
2) In the next hour a bridge to Cormaya opens, and a cake of 4 layers appears there. In less than 30minutes each layer has to be eaten to be able to eat the next one, because every 30 minutes if the layer has not been eaten all the characters in the cake are teleported outside and the layer is reseted.
In order to eat the cake, your character need to be 'hungry', and even if it is completly hungry, it will be only able to do 4 bites, so a lot of people is needed to complete this part of the event.
Other option is to bring low lvls characters with residence on edron or farmine, and kill them, so they come back to eat the cake once and other and other time, since after a death your character is always hungry.
Hope I helped with my answer