Here are the combined sentences using noun clauses:

1. **Is there an ATM near here? Could you please tell me?**
- **Combined:** Can you please tell me if there is an ATM near here?

2. **The train will arrive at a certain time. Do you know the time?**
- **Combined:** Do you know what time the train will arrive?

3. **Where did Sarah go last night? Do you know?**
- **Combined:** Do you know where Sarah went last night?

4. **He may be innocent. I don’t know.**
- **Combined:** I don’t know if he may be innocent.

5. **Where is the nearest supermarket? Could you please tell me?**
- **Combined:** Can you please tell me where the nearest supermarket is?

6. **She may have told the truth. She may not. It remains doubtful.**
- **Combined:** It remains doubtful whether she may have told the truth or not.

7. **He distrusts his own son. It is difficult to understand the reason.**
- **Combined:** It is difficult to understand why he distrusts his own son.

8. **How do you operate this new machine? Could you explain?**
- **Combined:** Could you explain how to operate this new machine?

9. **He behaved very rudely at the party. It’s unforgivable.**
- **Combined:** It’s unforgivable that he behaved very rudely at the party.

10. **We've met this girl before! You forgot.**
- **Combined:** You forgot that we've met this girl before.

### Explanation:
A noun clause functions as a noun within a sentence. To combine the sentences, we identify questions or statements that can be turned into noun clauses, typically starting with "if," "what," "where," "whether," etc. This allows us to effectively combine information from both sentences into a single coherent sentence.