title: How to find the prefix of the bot inside a Cog when storing prefix in a json file
body: <p>I want to have my Discord bot reply to a ping. And I would like to add the prefix of the bot along with the reply.</p>
  <pre><code>@commands.Cog.listener()
  async def on_message(self, message= str):
  
    with open('prefixes.json', 'r') as f:
      prefixes=json.load(f)
    prefix=prefixes[str(self.guild.id)]
    
    #reply to a ping
    if self.bot.user.mentioned_in(message):
        await message.channel.send(f'Hey there, my prefix is `{prefix}`. Please enter `{prefix}help` for a more detailed overview!')
  </code></pre>
  <p>The error I'm getting:
  AttributeError: 'Events' object has no attribute 'guild'</p>