Where would my transmission fluid tank be in my Honda Civic DX hatchback?

Where would my transmission fluid tank be in my Honda Civic DX hatchback?

You seem to be quite confused. NO vehicle has a "transmission fluid tank", and you also fail to specify whether your beater has a manual or automatic transmission.

If you somehow think the transmission needs to be checked, take it to the dealership or other friendly, competent shop (or knowledgeable friend or neighbor) and have them show you how it's done.

The "Transmission fluid tank" is the transmission itself.

In the transmission

It does not have a tank. The case is the reservoir. There's a single dipstick on that tans. That is all that you need to check. That one is checked with the engine off and the trans warm.