1. "I'm not sure."
2. "I don't have that information."
3. "I don't know off the top of my head."
4. "I'm afraid I can't answer that right now."
5. "I'm not familiar with that."
6. "I don't have that detail at the moment."
7. "I don't have the answer to that question."
8. "I haven't looked into that yet."
9. "I'm not aware of that."
10. "I don't have that in my knowledge base."