Question

1. Do you ask what it was?

2. Do you tell what it was?
3. Do you remember what it was?

4. What do you suppose it was?
5. What do you imagine it was?
6. What do you believe it was?
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Are they all grammatical?

Answer 1

All are grammatically correct, but 1 and 2 are very awkward and not used. The rest are fine.