Since you are communication using a web-connection you need a ip-address. Ip addresses are usually not anonym because they are bound to a contract. There are some restrictions: You could use a web-cafe for example and use this way the ip-address bound to a contract of the owner of the web-cafe.
Since slack is using TLS you have "some&...
Your app will need to subscribe to reaction_added event. Once subscribed, you'll receive this event each time a reaction is added to a message visible to the bot. This means, this you'll receive the event for the channels where the bot is a member. Or direct messages sent to/by the bot.
If you specifically want to process events where the message was sent by ...
You can type / in the compose message panel. Slack gives you a list of slash commands available. The top one is the last command used.
Once you select it (or press enter), you can edit the command if you wish.