Do i need rug backing if the rug is on carpet?

Usually carpets have some weight to them which prevents them from going anywhere when on carpet. I know the latch hook rug you are talking about. I used to make them when I was younger. These aren't particularly heavy so you might need something to hold it in place. Depends on the size too. I wouldn't use any type of glue on the rug. You can buy little disc like things from carpet or hardware stores to stop the rug from moving. They have little nodules on them and they kind of dig in to both sides without damaging either the rug or the carpet.