for anyone stumbling upon this from my profile: this was a code review for someone's first Discord bot as a complete beginner to JavaScript :)

index.js

const Discord = require("discord.js"); 
const TOKEN = "TOKEN";
const { Client, RichEmbed } = require('discord.js');

// Why do you require discord.js twice? the require call in line 1 is redundant

var bot = new Discord.Client();

// since you required Client explicitely, you could do new Client() instead of new Discord.Client();
// var is kinda deprecated, I suggest you use const, as the bot variable doesn't change in the future
// bot is not really what this represents; the bot is so much more than just the discord client instance, hence the name client would be more fitting for the variable

bot.on("ready", function() { // try to stick to a consistent quote style - either always doubles, or always singles
    console.log('ready');
});

bot.on("message", function(message) {
    if (message.content === "activateBot") {
        const embed = new RichEmbed()
            .setTitle('Music Bot Control Panel')
            .setColor(0x00FF00) // latest discord.js also supports '00FF00' if I'm not mistaken, instead of the hex literal
            .setDescription('Control the Bot using the Reaktions!');
        message.channel.send(embed);
    }
    if (message.embeds[0] && message.author.equals(bot.user)) { // you could do this directly after sending the message, instead of waiting for the next message event
        message.react("⏮")
            .then(() => message.react("▶"))
            .then(() => message.react("⏸"))
            .then(() => message.react("⏭"));
    }
});

bot.on('messageReactionAdd', (reaction, user) => {
    if (!user.bot) { // maybe this could be if (user.bot) return; to not have everything inside an if clause
        if (reaction.emoji.name === "⏮") {  // here, possible switch/case could be used for cleaner code
            reaction.message.channel.send('!back');
        }
        if (reaction.emoji.name === "▶") {
            reaction.message.channel.send('!play');
        }
        if (reaction.emoji.name === "⏸") {
            reaction.message.channel.send('!pause');
        }
        if (reaction.emoji.name === "⏭") {
            reaction.message.channel.send('!next');
        }
        reaction.remove(user);
    }
});

bot.login(TOKEN);

// a wise man once told me to always add a newline after the end of a file because it confuses some interpreters


// What i like; the indents are consistent and logical, some variable names like embed are clear and concise, as well as set to be constant which makes sense.