This a case of composite supply where rate of tax will depend on supply of predominant product or supply. In this case gold is supplied as predominant item and making charges is naturally bundled. So gst rate for making charges will be the rate of gold.
GST rate on gold jewellery is 3%.(in case of regular dealer)
Final price of the jewellery = Price of (22 KT or 18 KT) gold X (Weight in grams) + Making charges + GST at 3% on (Price of jewellery + making charges).