Is departure tax reported on my regular T1 return or a separate form?

Departure tax is reported through your regular T1 return for the year you emigrate, not through some entirely separate tax filing outside the ordinary system. The deemed disposition itself is worked out on Form T1243, which calculates the capital gains and losses on the property affected, and those results then flow into your T1 return for that year the same way any other capital gain or loss would.

Alongside T1243, you may also need to file Form T1161 disclosing the property you owned at departure, and both forms are filed together with, not instead of, your regular return for the departure year. There isn't a standalone "departure tax return" separate from your normal annual filing, instead, your ordinary T1 return for that specific year simply carries extra components reflecting the fact that it's also your departure-year return.

Because these forms have to be prepared and reconciled together correctly for a single return, and because the numbers involved, valuations, elections, and prorated credits among them, are more complex than an ordinary year, the departure-year T1 is genuinely one of the more involved returns most people ever file, worth preparing carefully rather than treating like any other year's filing.