In which stage of kidney disease does calcium deposits to form small lumps on skin? how i can tell those lumps are due to calcium deposits and not mosquito bites?

This occurs in late stages. Mosquito bites are usually pin-point red in color calcium beposits are deeper and not red

This usually happens when you are on dialysis (end stage kidney disease) and your Ca x PO4 is too high. In early stages of kidney disease, your PO4 could be high but usually Calcium is not high (unless you take too much vitamin D or calcium containing PO4 binder). If you are on dialysis, try to control PO4 well. Mosquito bite usually causes a red papule then itching but it will resolve in 1-3 days