How many times do you have to defeat the cog bosses to earn the key to cogtown?

To earn the key to Cogtown in "Toontown," you need to defeat each of the cog bosses a total of three times. This task involves defeating the bosses in their respective areas, which include the Sellbot, Cashbot, Lawbot, and Bossbot headquarters. Once you've completed this requirement, you'll receive the key, allowing you to access Cogtown.