If someone says "Any questions?" and you have no question in your mind, you can say many things. To be abrupt you can just say "No", but to be more friendly or polite you can say "No, that's very clear, thank you". or "None, I'm happy with that, thanks". or "Not at the moment, but if I think of any I will ask later". or just "no, but thank you". Your answer can be quite flexible.

You can also say 'none at the moment, thanks!' 'No everything 's clear so far, thanks'

yoo should said ： Mm......