1.What are you doing?
2.When did many dinosaurs live?
3.Where does a giant panda live?
4.How long is a blue whale?

Donny: When did many dinoshar live?
Correct: When did many dinosaurs live?
Explanation: Be mindful of the word spelling. If you're not sure about it, consult a dictionary.

Donny: How long is blue wheal?
Correct: How long is a blue whale?
Explanation: Again, be mindful of the word spelling. The article 'a' is used because you are referring to any blue whale.

Note: Hi Donny! Be mindful of the word spelling because it is important to understand your sentence. Anyway, you did a good job. Keep it up!