Expected end to close function near elseif, how to fix this?

Well, it's most a matter of organization, so you can find the missing ends and fix your if conditions. But I think you should get to know Conditional statements better, because this script is pretty messed up.

I didn't get the purpose of these many conditions, but I organized and fixed your script as I usually do. So, a working code would look like this:

local mouse = game.Players.LocalPlayer:GetMouse()
target1 = nothing
target2 = nothing
target3 = nothing
target4 = nothing
target5 = nothing
mouse.Button1Down:connect(function()
	local part = mouse.Target

	if part.Parent:FindFirstChild("Humanoid") ~= nil then
		print("Humanoid!")
		local humanoid = part.Parent:FindFirstChild("Humanoid") 
	end -- missing end

	if script.Bools.Target1.Value == false then
		target1 = part.Parent.Name
		script.Bools.Target1.Value = true
		script.Bools.Target1.TargetName.Value = (part.Parent.Name)
	elseif -- the elseif is in the if block
		script.Bools.Target2.Value == false then
	end -- missing end

	if part.Parent.Name == target1 then
		-- something here
	elseif
		script.Bools.Target3.Value == false then
	else -- you should put the else last
		target2 = part.Parent.Name
		script.Bools.Target2.Value = true
		script.Bools.Target2.TargetName.Value = (part.Parent.Name)
	end

	if part.Parent.Name == target1 or target2 then
		-- something here
	elseif script.Bools.Target4.Value == false then
		-- something here
	else
		target3 = part.Parent.Name
		script.Bools.Target3.Value = true
		script.Bools.Target3.TargetName.Value = (part.Parent.Name)
	end

	if part.Parent.Name == target1 or target2 or target3 then
		-- something here
	elseif
		script.Bools.Target5.Value == false then
	else
		script.Bools.Target4.Value = true
		script.Bools.Target4.TargetName.Value = (part.Parent.Name)
	end
	
	if part.Parent.Name == target1 or target2 or target3 or target4 then
		-- something here
	else
		target5 = part.Parent.Name
		script.Bools.Target5.Value = true
		script.Bools.Target5.TargetName.Value = (part.Parent.Name)
	end
end)