I have a doubt regarding the end of the sentence, can you help me?:
-"Your new haircut is great. You look 20 !/ You look like you're 20!"
What is your doubt?
Either one works.
In English the words doubt and question do not have the same meaning.
"I have a question about this food." This means that I want to know how the food is prepared or what the ingredients are, etc.
"I have a doubt about this food." This means that I think the food may be spoiled, bad-tasting, or unhealthy.
Doubt always implies a negative connotation.