There are a number of good online resources to help people reflect on their own hidden bias and prejudice. I have several posted on my mainstream Social Studies page under Prejudice.
Project Implicit, a series of quizzes, is from Harvard, and may the most well-known online resource for discovering hidden bias. It’s probably accessible to Intermediate English Language Learners.
Teachers might also find the Scientific American article, Buried Prejudice: The Bigot In Your Brain, helpful.