Здесь в первом случае, в принципе, возможно оба варианта, но больше приветствуется второй с to be going to...
I am going to the circus tomorrow.
1. Who will go to the circus tomorrow?/ Who is going to the circus tomorrow?
2. Will I go to the circus or to the show?/ Am I going to the circus or to the show?
3. It will be circus, won't it?/ Is it going to be the circus, isn't it?
4. It will be circus?/ Is it going to be the circus?
5. When will I go?/ When am I going to the circus?
The show starts at 7.
1.Does the show start at 7?
2. When does show start?
3. What does start at 7?
4. Does the show or the circus start?
5. Does the show start at 7, doesn't it?