How do I make it activate on click?

First thing first you need to add click detector inside the brick, and then you can use this script inside the brick. Here is the reference

local brick = script.Parent -- your brick
local click = brick.ClickDetector -- the clickdetector
click.MouseClick:Connect(function() --When you click the brick then
--Do what you want here
end)

i think this is the right code

local Cooldown = false
local brick = script.Parent -- your brick
local click = brick.ClickDetector -- the clickdetector
click.MouseClick:Connect(function(Player)
    if Cooldown == true then return end
    if Player:IsInGroup(script.Parent.IsRestricted.Value) then
        if not Player.PlayerGui:FindFirstChild('NYPDBookPlayer') then
        if Player.Backpack:FindFirstChild('Grab') then
            if Player.Backpack.Grab.Suspect.Value then
                if game.Players:FindFirstChild(Player.Backpack.Grab.Suspect.Value) then
                    local Gui = game.ServerStorage.NYPDBookPlayer:Clone()
                    Gui.Parent = Player.PlayerGui
                    Gui.Suspect.Value = game.Players:FindFirstChild(Player.Backpack.Grab.Suspect.Value)
                    end
                end
            end
        end
    end
    Cooldown = false
end)    

as i see here, you have a thing with remote event and i dont know where the fireserver(). So if you need to make a click detector inside a brick then you only need to do like i said earlier Let me know if it helps