Answers for "discord py how to get who send the mes"

discord.py add reaction to message

#1
message = ctx.send("text")
#2
message = channel.send("text")
#3
message = channel.fetch_message(messageid)
#add reaction to message
emoji = 'N{THUMBS UP SIGN}'
await message.add_reaction(emoji)

discord py fetch channel by id

channel = discord.utils.get(ctx.guild.channels, name=given_name)
channel_id = channel.id