Similar to Tenka's UMK3 Tower guide (of which I have stolen parts of) here's one for MKT.

Each Tower has a fixed order of characters, and it is random which Tower you will get. It is assumed that each one has an equal chance of showing but we currently have no confirmation of this.

The towers are named based on the character below the first endurance match (the exception to this being the 2 "Robot Smoke" towers, which are still named after Robot Smoke, but also the character found below him on said tower). Once you see that character when selecting your Tower, you can use this information to deduce every character you will face in the Tower and their order all the way until the final Shao Kahn fight.

THE ROBOT SMOKE/CYRAX TOWER Human Smoke Noob Saibot Kitana Jax Cyrax Robot Smoke E1 - Rain, Stryker, Ermac Goro E2 - Ermac, Kintaro, Reptile Motaro

THE LIU KANG TOWER Scorpion Classic Sub-Zero Kitana Old Jax Rain Robot Smoke Liu Kang E1 - Reptile, Nightwolf, Rain E2 - Ermac, Kintaro, Reptile Motaro

THE ROBOT SMOKE/SINDEL TOWER Classic Sub-Zero Mileena Ermac Reptile Jade Sindel Robot Smoke E1 - Old Jax, Jax Goro E2 - Kintaro, Motaro

THE KANO TOWER Scorpion Ermac Noob Saibot Reptile Liu Kang Sonya Kano E1 - Ermac, Mileena, Classic Sub-Zero E2 - Goro, Kintaro Motaro

THE KABAL TOWER Ermac Nightwolf Reptile Liu Kang Old Raiden Scorpion Kabal E1 - Scorpion, Ermac, Rain Kintaro E2 - Baraka, Motaro

THE KUNG LAO TOWER Ermac Jade Unmasked Sub-Zero Noob Saibot Sindel Nightwolf Kung Lao E1 - Sektor, Reptile, Rain, Cyrax, Noob Saibot E2 - Goro, Kintaro Motaro

I'm not sure if there are more, but if I missed any, let me know, and I'll make amendments.