Prompts can be visual, spoken or written.
Example
The learners are asking each other about their food likes and dislikes. The teacher puts photos of various foods up on the board as prompts for their questions.
In the classroom
Resources that can be used as prompts include flashcards, realia, body language, facial expression (for correction), key words, questions, repeating errors, and other learners.
See also:
https://www.teachingenglish.org.uk/article/flashcards-0
https://www.teachingenglish.org.uk/article/realia
Further links:
https://www.teachingenglish.org.uk/article/speaking-aids