How do i fix "attempt to index nil with parent"?

This is due to the fact that player characters are not Archivable by default. If an Instance is not archivable, something:Clone() returns nil.

The solution would be to make the character archivable.

OnServerEvent:Connect(function(player)
    local character = player.Character
    character.Archivable = true
    local clone = character:Clone()
    -- etc
end

Unfortunately, the only way to clone a character is to use Players:GetCharacterAppearanceAsync or Players:GetCharacterAppearanceInfoAsync. I'll shorten these to GetCharacter and GetCharacterInfo because they're hard to type.

GetCharacter returns a model full of these assets. Keep in mind that it does not return an NPC model. It returns the assets. So if you wanna get the Appearance, do this:

script.Parent.OnServerEvent:Connect(function(plr)
    local model = game.Players:GetCharacterAppearanceAsync(plr.UserId) --You need a UserId.
    model.Parent = workspace --Recommend you parent it to workspace to see the properties. This is only an example.
end)

However, if you prefer a table, use GetCharacterInfo. However, it uses Dictionaries and sub-assets, which makes it harder to use. Don't recommend this one unless you don't wanna spam assets.

script.Parent.OnServerEvent:Connect(function(plr)
    local table = game.Players:GetCharacterAppearanceInfoAsync(plr.UserId)
    for i, v in pairs(table) do
        print(i , v) --Recommend you do to get the table of contents.
    end
end)

Also, turning off Archivable may result in exploits on the client. So I don't recommend it at ALL.