One word:ANYWHERE.
get the watering can thing and spray sudowoodo... after beating the gym.
it is where if you leave to go to the next town it is blocking the road or out of the park to the east
After you beat Whitney go to the flower shop in goldenrod then she will give you a squirtbottle then you go to the road towards ecruteak city and sudowoodo will be blocking your path talk to it and than your character will squirt the bottle then you battle sudowoodo and its at level 20
You can`t find him in firered unless you decide to get the two rare stones for celeo. Then, you can go to the upper floors of pokecenter and then you go to trades and you trade with POKEMON EMERALD VERSION. This is the only way to get Sudowoodo in firered. No need to thank me [:-)You need to trade one from Silver or Gold, there is no native Sudowoodo in FR/LG.
in route 36 theres a tree get the squirtbottle after defeating Whitney in the flower shop next to the gym pour it on the odd tree and there you go theres the lv 20 sudowoodo
Go to the Key Items pocket in your bag, press "Use" and you will be able to use it. For doing on the Sudowoodo blocking your way to Ecruteak City, just press "A" when your close enough to the Sudowoodo.
beat goldenrod gym and then go to the flower shop and get the squirtbottle and thn spray it on the sudowoodo and you can battle it.
Go to the flower shop and talk to the lady there. She gives you a squirt bottle. Use it on the tree and you get a chance to catch sudowoodo.
To get to Ecruteak City, you need to defeat Whitney (the gym leader of Goldenrod) and then talk to the girl in the house next to the gym. She'll give you a Squirtbottle to rid the Sudowoodo on Route 36 and get to Ecruteak. My game, however, has a glitch that allows you to go to Ecruteak, Olivine, etc. before beating Whitney. To do so, go in front of the Sudowoodo and into your party and select Cut from one of your Pokemon. BAM! The Sudowoodo is killed.
Defeat the Goldenrod GYM leader Whitney and then go to the little house next to the GYM and talk to the lady and she will give you a squirtle bottle and you use that on Sudowoodo
Use the squirtbottle on it it will attack its sudowoodo capture it or defeat it and it will go away.
Go to the ruins of alph near the sudowoodo. If you get inside the right building you can.