I am having a doubt
I am having a doubt
Indian English: I have a question about this.
Ma'am, I am having a doubt in question five.
I have a question
Works everywhere: you want something explained.
Excuse me, I have a question about question five.
Remember: Clear in India; outside India, 'doubt' sounds like distrust. Say 'I have a question' or 'I'm not sure about…' so everyone follows.