Anything you want! It's your Pokémon after all.
it should be giritina
Go to Lavender Town, the one with the Pokemon Tower. There should be a house where you can change your Pokemon's name. There should be a sign near the house saying Name-Rater. you go to Lavender Town and look for a house that says Name-Rater
It should give you an option to after you catch it
Grant
You should keep the name Lugia
Unfortunately there is no way to change the name of your human character once you have chosen it. To change the name of your Pokemon, the name rater should be in Goldenrod next to the Pokemart.
As of the 6th generation games (X and Y, Omega Ruby and Alpha Sapphire), there are 719 different species of Pokemon.
If you're Pokemon has another evolution then after it evolves you should be able to change its name if it doesn't I suppose you could always breed the Pokemon. (considering its not a lengendary Pokemon).
HERE is a good anime/manga name generator for you.
The Name Rater is in Eterna City. He is in an apartment building near the Pokemon mart, on the first floor. There should be a sign outside of the building mentioning Name-Rating.
The Name Rater should be located in Lavender Town.
maybe if a boy, cyndo and if a girl, cynda