In an ELT classroom, this can mean questions teachers ask learners and learners ask each other. Referential questions can be compared to display questions, for which the answer is already clear and teachers ask just to see if the learners know the answer, or for language manipulation.
Example
The teacher asks a learner ‘What did you do at the weekend?', or a learner asks another ‘Why are you so sad?'
In the classroom
Extended activities in which learners can practise production of referential questions include quizzes (setting and answering questions), interviews, discussion of work in the class, and posting questions on general knowledge forums.
See also:
https://www.teachingenglish.org.uk/article/display-questions
Further links:
https://www.teachingenglish.org.uk/article/asking-questions
https://www.teachingenglish.org.uk/article/question-techniques-strategies
https://www.teachingenglish.org.uk/article/why-do-we-do