India taxes the gain, and the treaty does not help
Start with the UAE side, which is the easy half: the UAE has no personal income tax and no capital gains tax, so selling your Indian property triggers no UAE tax on the gain. All of the tax is on the Indian side. If you held the property for more than two years, the gain is long-term and taxed at 12.5 per cent, without indexation. It is worth knowing that as an NRI you do not have the alternative of 20 per cent with indexation, that option is only for resident individuals, so your gain is simply the sale price minus your cost, at 12.5 per cent.
People often hope the tax treaty will reduce this, but it does not. Under the India-UAE treaty, gains on immovable property situated in India are taxable in India, because property is taxed where it sits. So there is no treaty rate to claim on a property sale, India taxes the gain in full, and a UAE tax residency certificate, useful for your other Indian income, does nothing for the property gain itself. The lever on a property sale is not the treaty, it is the withholding certificate.
The withholding trap, and the fix
The trap that catches nearly every NRI seller is the withholding. When an NRI sells, the buyer must deduct TDS under Section 195, the section for payments to a non-resident, not the 1 per cent that applies when the seller is resident. And in practice buyers, and their advisers, deduct that TDS on the entire sale consideration, not on your actual gain. On a property that has barely appreciated, that can mean a large chunk of the whole price is withheld against a small real tax, and you wait to reclaim the excess through a return.
The fix is to get ahead of it. Before the sale, you apply for a lower-deduction certificate, under what is currently Section 197 and becomes Section 395 under the new law, which tells the buyer to withhold only on the actual gain at the right rate, rather than on the full price. That single step frees up most of the cash the crude withholding would otherwise trap. Alongside it, reinvestment reliefs under Sections 54, 54EC and 54F can reduce or defer the gain if you put the proceeds into another house or specified bonds, and the net proceeds repatriate out of your NRO account within the yearly limit. Getting the certificate, the reliefs and the repatriation right is the whole job on a UAE-resident sale, and it is the Indian side we handle.