How Do i Check Who Invited Who Discord.js

There is no easy built in way to do this, so instead you'll have to store the number of uses of every invite, then when somebody joins, see which invite's uses doesn't match the last known number, ie seeing which invite's use count changes.

client.invites = {}

client.on('ready', () => {
    client.guilds.cache.each(guild => { //on bot start, fetch all guilds and fetch all invites to store
        guild.fetchInvites().then(guildInvites => {
            guildInvites.each(guildInvite => {
                client.invites[guildInvite.code] = guildInvite.uses
            })
        })
    })
})

client.on('inviteCreate', (invite) => { //if someone creates an invite while bot is running, update store
    client.invites[invite.code] = invite.uses
})

client.on('guildMemberAdd', async (member) => {
    const channel = member.guild.channels.cache.get('CHANNEL_ID');
    member.guild.fetchInvites().then(guildInvites => { //get all guild invites
        guildInvites.each(invite => { //basically a for loop over the invites
            if(invite.uses != client.invites[invite.code] { //if it doesn't match what we stored:
                channel.send(`Welcome ${member.user.tag} Invited By ${invite.inviter.tag}`)
                client.invites[invite.code] = invite.uses
            }
        })
    })
})

You should add some sort of check (which I admittedly should have done), as they could have used a vanity URL or server discovery or some other strange way of joining, in which case it would probably error.