Datastore leaderboard isn't working?

You have a very tiny error on line 11: you haven't provided a key to GetAsync. Additionally, you're incorrectly saving the two leaderboard stats on line 24.

Also, rather than calling GetAsync twice, it's better to store the result of the first call, and then check if it exists:

--The 'or nil' is necessary here: https://scriptinghelpers.org/questions/461/
local stats = DS:GetAsync(key) or nil
if stats then
    cash.Value = stats[1]
    job.Value = stats[2]
else
    --...
end

Alternatively, you can reduce that if into two lines:

local stats=  DS:GetAsync(key) or nil
cash.Value = stats and stats[1] or 0
job.Value = stats and stats[2] or "None"

SetAsync only takes one Value after the provided Key, not multiple. Plus, you're using the return like it's a Table anyway:

DS:SetAsync(key, {cash.Value, job.Value})
--Notice the curly braces.

There are two problems with your code :-

    local key = "plr_"..plr.UserId
    if DS:GetAsync(key) then -- you check the ds here but don't use the result this is a waste of requests
        local stats = DS:GetAsync() -- you have not given the key
        cash.Value = stats[1]
        job.Value = stats[2]
    else
        cash.Value = 0
        job.Value = "None"
    end

game.Players.PlayerRemoving:connect(function(plr)
    local stats = plr.leaderstats
    local cash = stats.Money
    local job = stats.Job
    local key = "plr_"..plr.UserId

    DS:SetAsync(key, cash.Value, job.Value) -- when saving multiple data it needs to be as a table
end)

Saving multiple values using a Table

The final result:-

local DS = game:GetService("DataStoreService"):GetDataStore("Save")
game.Players.PlayerAdded:connect(function(plr)
    local stats = Instance.new("IntValue", plr)
    stats.Name = "leaderstats"
    local cash = Instance.new("IntValue", stats)
    cash.Name = "Money"
    local job = Instance.new("StringValue", stats)
    job.Name = "Job"
    local key = "plr_"..plr.UserId

-- make a variable of the data once
     local stats = DS:GetAsync(key)
    if stats  then
        cash.Value = stats[1]
        job.Value = stats[2]
    else
        cash.Value = 0
        job.Value = "None"
    end
end)
game.Players.PlayerRemoving:connect(function(plr)
    local stats = plr.leaderstats
    local cash = stats.Money
    local job = stats.Job
    local key = "plr_"..plr.UserId

    DS:SetAsync(key, {cash.Value, job.Value}) -- this Is now in a table format
end)

Hope this helps.