Looking on the internet deeply has found these results:

I have a question is the most popular phrase on the web.

I have a doubt 138,000,000 results on the web	I have a question 1120,000,000 results on the web More popular!
Some examples and use cases from the internet:	Some examples and use cases from the internet:
I have a doubt about the compatibility of products; whom can I ask? Swami, I know that I am crossing my limits, but please excuse me. I have a doubt here. Come to think of it, I have a doubt. I have a doubt: it's Professor Tommasi? Link near the I have a doubt about Privacy Policy.Who can I contact? If I have a doubt about how to do something: What color would you see as a background? When I have a doubt I wonder what Marco Travaglio would do. Thank you, the tutorial is excellent, but I have a doubt:	I have a question regarding the bake sale. Because I have a question for you, old bean. I have a question for you, Drake. Severus, I have a question for you. I have a question about the patents on the new synthetic. Finally I have a question about the European Fund for Refugees that was mentioned. And since we're compacted I have a question. I have a question I want him to answer.

I have a doubt

138,000,000 results on the web

I have a question

1120,000,000 results on the web

More popular!

I have a doubt about the compatibility of products; whom can I ask?
Swami, I know that I am crossing my limits, but please excuse me. I have a doubt here.
Come to think of it, I have a doubt.
I have a doubt: it's Professor Tommasi?
Link near the I have a doubt about Privacy Policy.Who can I contact?
If I have a doubt about how to do something: What color would you see as a background?
When I have a doubt I wonder what Marco Travaglio would do.
Thank you, the tutorial is excellent, but I have a doubt:

I have a question regarding the bake sale.
Because I have a question for you, old bean.
I have a question for you, Drake.
Severus, I have a question for you.
I have a question about the patents on the new synthetic.
Finally I have a question about the European Fund for Refugees that was mentioned.
And since we're compacted I have a question.
I have a question I want him to answer.