Yes, it is a deemed disposition, but the gain still needs to be reported because the TFSA is a tax sheltered vehicle. That said, if you had a loss, you won't be able to claim it.
The box 20 generally don't show up on your slip. Most financial institution doesn't keep track of the cost of your securities. You need to manually go through your statements and track down when you bought those securities and the price you bought it at and put that amount into box 20. It is possible that you bought them a few years ago, so you will need to track down the statements for a few years ago to get the cost amount.
Sometimes if you call your financial institution, they can send you a summary of all your transactions. This may help you track down the cost. Or if you can log into your trading account, you may be able to go back through your transactions to determine the cost of those securities.
