Hello. Here's the answer to your question.
The answer is Which was the strangest thing you have eaten?
When we ask a question, we often say Do you know...? / Could you tell me...?
etc. If you begin a question like this, word order is different from a simple question.
Where has Tom gone? (simple question)
but Do you know where Tom has gone?
(not Do you know where has Tom gone?
When the question is part of a longer sentence, it loses the normal word order.
Don't be afraid to ask if you don't know which to use. Hope my answer is sufficient.
HAve a nice day!